Avril Lavigne waited five years to return to the road -- and when she did, the preparation process was a scramble. She needed new guitars and straps, as well as a refresher on the bridges of hits like “My Happy Ending” and “When You’re Gone.”

“It’s funny,” the 34-year-old Lavigne tells Billboard. “I’m relearning, but it’s total muscle memory. I’m like, ‘Wait, it goes like this, right?’ Then without even trying I’m like, ‘It’s right here.’” (Even so, she always has a teleprompter onstage, “just in case.”)

Since the pop mainstay -- who has sold 12.5 million albums in the United States, according to Nielsen Music -- wrapped her Avril Lavigne Tour in Japan five years ago, she largely stepped out of the spotlight as she battled Lyme disease. For a long time, Lavigne (who at one point was bedridden) wasn’t sure if she would ever release another album or be physically able to tour again. Now that she has recovered, Lavigne says her 15-date trek that began in mid-September and runs through Oct. 11 in support of her long-awaited album, Head Above Water (which hit No. 13 on the Billboard 200 in February), is her most intimate yet.

“I was wondering what I was going to be doing, and unsure if I could work or not -- and songs just flowed,” recalls Lavigne. “After everything I went through, I re-fell in love with music all over again.”

The tour largely pulls from material off the intense, emotive Head Above Water, and its visuals are inspired by the album’s title track and the single “I Fell in Love With the Devil,” playing on the contrasting themes of water and fire.

“Devil” has been part of her encore, and a “really special moment” complete with a red dress and lots of fire. But still, Lavigne says that the tour is nostalgic, for both the audience and herself: there are wardrobe changes inspired by her music videos, and familiar imagery to appear in her visuals, like the “Sk8er Boi” star from debut album Let Go or the “Girlfriend” skull and crossbones from The Best Damn Thing.

“The singles from the last 17 years all hold memories,” she says. “‘Sk8er Boi’ is a moment, ‘Girlfriend’ is a moment -- and I get to go back with [my fans] and enjoy that.”

Lavigne counts Billie Eilish as a fan, along with a handful of indie artists on the rise like Soccer Mommy and Snail Mail. She recently met Eilish and her brother, Finneas, at Los Angeles’ Greek Theater during one of their hometown shows, and Lavigne recalls pulling up to the venue only to see her own face plastered on posters and screens promoting her upcoming date there.

“It’s an honor any time -- especially someone as talented and cool and creative as Billie -- mentions that I’ve had an impact on their music career,” says Lavigne. “My approach was always just like, I’m going to be myself, write the songs that I want to write, dress how I want to dress -- because when I entered the industry, everyone was showing their bellies and had a bunch of dancers around them and were bubblegum pop, and I was so different. I was dressing in Dickies and Converse and like a dude, and playing loud guitar in my songs.”

Lavigne sees a lot of similarities in Eilish, “who is her own individual,” which is largely why Lavigne thinks she’s taken off in such a major way.

“We’re in a time now where people want real, and they want authentic and they can read past the bullshit,” she says. “That was something I always stood my ground on, and I always fought to be true to myself. And she’s an artist who is very much herself, and also extremely talented -- and that’s why it’s working for her.”

That combination of authenticity and talent remains successful for Lavigne, who on her current trek chose to play 3,000- to 5,000-capacity theaters -- saying that an up-close-and-personal atmosphere made more sense for a more serious project. “It’s vulnerable and raw and exposed, whereas in the past it was loud guitars and fist-pumping,” she says. “You’ll still feel that from me, but with everything I went through, it’s like, ‘Okay, I’m here. I’m alive.’ I’m gliding back into it. I’m just so grateful to God that I’m still able to actually work and have a life.”

A version of this article originally appeared in the Sept. 21 issue of Billboard.