Stevie Nicks, legendary singer-songwriter and hard-living Fleetwood Mac frontwoman, is considering her greatest regret. It is not her "huge cocaine period", the 10 years that elapsed between the making of Fleetwood Mac's 40m-selling 1977 album Rumours and the moment, in 1986, when she finally entered the Betty Ford Center. Nor is it her complicated history with band members: she joined Fleetwood Mac in 1974 with guitarist Lindsey Buckingham, subsequently detailing their split in the hit song Dreams, and went on to have an affair with drummer Mick Fleetwood, which inspired the 1983 solo song Beauty And The Beast.

It is not even the eight years she lost to Klonopin, a prescription tranquilliser to which she became addicted in the late 80s and early 90s, when she was "just a sad girl, sitting in a big, beautiful house, going, 'What the f- hell happened?'"

The regret that has really stayed with her is her marriage, in 1983, to Kim Anderson, widower of her best friend Robin Snyder. Snyder's baby Matthew had been born two days before she died of leukaemia. Three months later, Nicks and Anderson were married.

"It was insanity," the 62-year-old says now. "Everybody was furious. It was a completely ridiculous thing. And it was just because I had this crazy, insane thought that Robin would want me to take care of Matthew. But the fact is, Robin would not have wanted me to be married to a guy I didn't love. And therefore accidentally break that guy's heart, too."

Nicks, now a multimillionaire, may have remarkable recall for details and dates from her four decades in music, but she also betrays the hallmarks of 70s cosmic thinking. She describes how she became aware of Snyder's displeasure: "One day when I walked into Matthew's room, the cradle was not rocking," she says. "I know that sounds crazy, but it was always rocking whenever I'd walk in, and I knew Robin was there. And one day it wasn't rocking and it was very dark and the baby was very quiet. And I said, 'Robin wants this to end – now.' I felt it as strongly as if she'd put her hand on my shoulder."

So it was a sign from beyond the grave?

"It was absolutely a sign."

Nicks had visited Snyder during her cancer treatment. "I was so high on coke. I'd drink half a bottle of brandy on the way there, 'cause I couldn't stand it. She was so sick. And she said to me, 'Don't come back until you're not high – don't come back into this place where everybody is dying.'"

Nicks shrugs. "So that was the Robin who would have said [of the marriage], 'You've lost your mind. What were you thinking?'"

Nicks and Anderson divorced after three months.

Stevie Nicks is holding court in a hotel suite with spectacular views of the ocean off Miami, as her tiny terrier, Sulamith, yaps about in a blue sweater. She is here for the Heart & Soul tour, a month-long series of concerts with Rod Stewart. The tour, billed as "Two legends – one stage", starts three days from now, but Nicks and Stewart have yet to rehearse together.

Stewart has been in the UK playing the proud, new, 66-year-old father to his eighth child. Nicks has been at her LA home, putting the finishing touches to her seventh solo album, In Your Dreams. It's her first new record in a decade. She and her producer/collaborator, former Eurythmic Dave Stewart, have spent a year in the mansion, writing, recording and filming vampire-themed promotional videos.

This afternoon, Nicks – 5ft 1in ("and a half"), blond and well-preserved – is agitated at the prospect of driving to Fort Lauderdale for her first practice with Rod the Mod. "Two hours it takes to get to! For probably 15 minutes of rehearsal!"

Only 15 minutes?

"Yeah, he's not a rehearser. He. Is. Not."

Because he doesn't need to?

"He doesn't care. He's just not like me. I'm like [I'm in] sixth grade: totally prepared, meticulous."

She is also relatively concert-ready: in 2009, Fleetwood Mac undertook a reunion tour of 83 shows around the world. Nonetheless, she says, "I'm scared, that's what I am. Rod's not scared. I have fear, he has no fear. And some people – me, Mick – we get panic attacks. Christine [McVie], too. That's why she quit." McVie, singer and ex-wife of bass player John McVie, left Fleetwood Mac in 1998 and now lives in the Kent countryside.

Since the tour, Fleetwood Mac's 1975 song Landslide – written by Nicks – has appeared in the US charts, though not in its original incarnation. "It's on Glee: Gwyneth Paltrow's done it," she says. "And it's number one!"

Nicks loves Glee, and American Idol ("My friend Steven Tyler's a judge now. I tell people, 'Two hours, don't call me, I'm watching Idol'"). She visited the Glee set during filming of the episode featuring Landslide, and creator Ryan Murphy has claimed Nicks asked him to write her a role in the series. "I did not," she says. "I don't really like to be filmed. But if I was ever going to do anything like that on TV, it would be Glee."

Nicks has strict rules about appearing on film. "I say, 'You gotta remember I'm 62 years old. So you've got to have those cameras up, and I have to have the best lighting in the world.' I'm not asking to look 16, I'm asking to look 40."

In the past, she has described the menopause as "horrible... rock and the menopause do not mix". Is that behind her now? "Well, kind of. My mom is 83 and she still has hot flushes. She just starts to sweat from the very top of her head. So there's parts of it that I feel don't ever go away. It's a way of life and you learn to live with it."

Does that make it harder to go on stage?

"No," she replies briskly, "because when you're on stage you have to forget about it. There is no dizzies, there is no cramps, there is no menopause. All there is, is the audience and what you do. So you feel great for those two hours. And when I come offstage, then I can burst into tears."

The new album opens with a song called Secret Love: "The ode to the rock star," as Nicks calls it.

Which one, though? Lindsey, Mick, Don Henley, his Eagles bandmate Joe Walsh? She shakes her head. "I'm not sure who I wrote it about. I wrote it in 1976. It's so old, I honestly cannot remember. In '75, '76, we were beautiful, fast, sexy, love was everywhere and we were moving from person to person. That's it. Love was around every corner."

In For What It's Worth, Nicks sings about a "forbidden romance that saved my life". It's not about Mick Fleetwood, she says. Rather, it refers to someone who stood by her in 1995, before the release of Fleetwood Mac's live album The Dance and after her stint in rehab for Klonopin.

It was "not a good time... I was freaked out. In rehab, when you're leaving, the last thing they say to you is, 'Don't get married, don't sign contracts, don't buy a house, don't sell a house. Nothing heavy.' Because your judgment is impaired. You're a shell. And you need to go out there and find out who you are, not on tranquillisers.

"So you walk out into the world and you are a different person. And we were going on a tour and I was terrified. Terrified. And this person just sort of hung with me through that tour and buffered me from the world. And he did save my life."

The Klonopin was prescribed by a psychiatrist to wean her off cocaine. While on it, her skin peeled off and her hair turned grey. "If someone ever says to you, 'I think you should take some Klonopin', you should get a gun and shoot yourself," she says.

As for the song Everybody Loves You ("We cause each other such pain... at home or on stage"), the music and chorus were written by Dave Stewart. He based it on one of 40 poems in Nicks's journal that she concedes is about Fleetwood Mac's guitarist. "And the reason Dave wrote the chorus the way he did was because of his relationship with Annie Lennox. So we had two duos. Dave understood. He's the same way with Annie – 'Everybody loves you... no one really knows you, I'm the only one' – I'm the only one that knew you before you were famous. So I let the song go ahead and be about Lindsey, and he let the song be about Annie."

Nicks and Buckingham met at high school in California and started out as a duo. Had Fleetwood Mac, fame and drugs not entered the picture, she believes, the couple would have stayed in San Francisco and had success anyway. "And we would have married and had children, 'cause we were headed that way. We didn't really mess up till we moved to Los Angeles. And that was when the whole world just ripped us apart."

Still, she says, "Fleetwood Mac was our destiny." But Buckingham doesn't feel the same way. "I think he regrets it totally. I think he wishes we hadn't ever joined Fleetwood Mac and had just stayed together. Even though his life has now wound around to where he's married to a lovely girl and he's got three absolutely beautiful kids."

Nicks, meanwhile, is happily single. "It's a decision I made, to not get married and have children," she says, "because I want to always be free to follow my art wherever it takes me."

She has no plans to retire, and thinks there will be another Fleetwood Mac album next year. She spends the rest of her time drawing, writing poetry and reading; her current obsession is the Twilight series.

One of her best friends, Sheryl Crow, recently adopted two boys, but Nicks isn't tempted by family life. "I want to have complete freedom. Sheryl does not have complete freedom now. She doesn't! But that's what she wanted. She wanted a baby. And I have a Yorkie Chinese crested dog. I'm happy with that."

• In Your Dreams is out on Warner Music on 27 June. Stevie Nicks will be at London's Hard Rock Calling on Sunday 26 June.