Genuine, non-snarky question: why is Avril Lavigne still here? You would have been a fool to bet against her original shtick being huge in 2002. An era in which Busted bestrode teenage affections like a tri-headed, invariably gurning colossus was clearly ripe for a Canadian teen dressed as a schoolgirl, sticking her tongue out, doing devil-horn fingers and peddling battery-farmed pop-punk aimed squarely at teens. And it was huge: her debut album Let Go sold 16m copies. Equally, however, you would have been brave to bet on Avril Lavigne hanging around. You could marvel at the precision-tooling that went into Sk8er Boi without thinking it was necessarily the stuff on which protracted careers were founded. A gap in the market had been identified and exploited, a great deal of money made, and its audience were bound to grow up and move on, right?

Wrong. Seventeen years on from Let Go and here we are, staring down the barrel of Lavigne’s sixth album. How has she survived, even flourished, when the careers of most 2002 teen sensations – and indeed the pop-punk bands that provided her initial inspiration – have withered? In the interim, certain adjustments have been made. Her albums now sell only in vast quantities, rather than figures that make you think there’s been a misprint. Her image has shifted. You can’t go on dressing like a schoolgirl and sticking your tongue out indefinitely, although Lavigne kept at it longer than you might imagine, bolstered by her 2007 single Girlfriend, a Chinn and Chapman-esque burst of bubblegum so brilliant it would have been a huge hit at any point in the last 50 years. By contrast, Head Above Water arrives with a cover that offers us Avril Lavigne, serious singer-songwriter, naked but for an acoustic guitar, a stock signifier of unvarnished honesty that, for some inexplicable reason, male singer-songwriters are never impelled to use to prove their sincerity.

In a sense, this approach returns Lavigne to her roots. Like a millennial equivalent of Gryphon, the medievally inclined prog band whose members ditched their crumhorns and regrouped as the Banned when punk hit, she was originally signed as a country-ish singer-songwriter, before someone noticed that Blink-182 were selling millions. Head Above Water’s title track, meanwhile, has been a big hit on US Christian radio, hailed as a powerful worship ballad: Lavigne’s career began with her performing alongside a Christian singer called Stephen Medd.

The reviewers at Faithwire and Christian Headlines have a point. Head Above Water is powerful, in a big old MOR power-ballad way. In fact, what the yanks call adult contemporary is very much the album’s most successful mode: it’s at its best when Lavigne and her co-writers forget about trends and roll out the booming drums and the kind of air-punching choruses you could imagine Heart singing in their garagantuan-haired 80s heyday. No one is ever going to describe the results as hip, but It Was in Me and Warrior are ruthlessly well-written, they fit Lavigne’s voice and the soldier-on lyrical sentiment is given a little edge by the album’s backstory. Head Above Water was inspired by Lavigne’s battle with Lyme disease, the tick-bourne infection to which she succumbed shortly after her 30th birthday and, she has said, nearly killed her.

Avril Lavigne: Head Above Water – video

It’s on substantially shakier ground when it tries to apply the pragmatic thinking that led Lavigne to co-opt pop-punk to what’s in vogue today. The sentiment behind Dumb Blonde – female empowerment anthemics featuring a guest appearance from Nicki Minaj and a guitar part that sounds like Stevie Nicks’ Edge of Seventeen – is inarguable, but it feels flat and rote. You could point out that Lavigne’s brand of empowerment doesn’t seem terribly empowering, relying as it does on reinforcing a lot of grim stereotypes about other women being dumb blonds and “stupid Barbie dolls”, but it hardly seems worth it; clearly no one involved in its manufacture considered the song that carefully. The problem with the album’s dabblings in chart pop à la Taylor Swift (Souvenir, Goddess, Bigger Wow) and post-Amy Winehouse retro-soul (Tell Me It’s Over) isn’t that the songs are poor, or that Lavigne can’t manage the stylistic shifts. It’s more that she doesn’t impose herself on them – they could be by anyone. You struggle to identify exactly what she’s bringing to the party beyond a knowledge of which way the commercial wind is blowing.

The end result isn’t bad, but it is uneven. For all the talk of Lavigne finally writing her life and telling her story it’s hard not to come away thinking that her heart lies more with the power ballads than the lunges for commercial contemporaneity. They are the songs that hit hardest and stick around. Still, the other stuff has its role to play, not least in answering our initial question. Why is Avril Lavigne still here? Perhaps because she’s more adaptable.

This week Alexis listened to

Unknown artist: Shelved Recordings #1

Two 12-ins in a generic sleeve with no track titles or details at all turn out to be luscious re-edits of obscure 80s pop tracks, smooth and weird in equal measure. Side 4 is the killer: a 1980 B-side by the otherwise unknown Lisa King, dreamily psychedelic perfect post-disco pop.