CHICAGO — With a toss of her hair and pop of her hip, Avril Lavigne smirked at her audience. “Don’t pretend, I think you know I’m d— precious,” she sang, delivering her “Hey Mickey”-esque 2007 single “Girlfriend.” “And hell yeah, I’m the (expletive) princess!”

She’s still a “princess” — a pop-punk princess, to be precise.

In 2002, 17-year-old Lavigne led the way for pop music to get a bit grungier, delivering a middle finger with chipped black nail polish, bubblegum sneer and skater aesthetic in place of the high-gloss, tightly choreographed, teen boy fantasy of the female pop star. Her debut album, “Let Go,” noted for its authenticity and viewed as an industry disruption, went four times platinum, making it the top-selling debut of the year while also inspiring an entire generation of young women to sport neckties with tank tops and, for many, becoming a gateway artist who gave them their earliest taste of punk’s influence.

That youthful, free-spirited delinquency continued to carry through the albums that succeeded “Let Go,” even as sweeping, lovelorn piano ballads worked to offset it. But in 2014, a year after releasing her self-titled fifth album and not long after her 30th birthday, Lavigne was diagnosed with Lyme disease and music was placed on the back burner. There was a time she, and her fans, thought she would die.

Five years later, Lavigne’s on the tail end of her “Head Above Water” tour — her first since being diagnosed — which hit the Chicago Theater Thursday night in support of her sixth studio LP (released in February) of the same name. It was also the eve of her 35th birthday — we know this because she was serenaded with “Happy Birthday” not once, but twice.

Opening her 75-minute set with the new album’s title track, the artist who once feared losing her voice sounded strong and clear in delivering the emphatic ballad, which she has said came to her as she lay in her mother’s arms, feeling as if she was drowning, like a fist-pumping fight song. While resilience was the theme of the evening, there was a noticeable sense of urgency to not dwell too much on the emotional intensity of her latest work. As soon as the song ended, even before the applause died down, the lights dimmed as Lavigne disappeared for an outfit change and her five-piece band plunged into an extended lead into “Happy Ending” from her sophomore album “Under My Skin.”

From then on, it was classic Avril — trading her flowing, white dress and tiara for guitar, leather-look pants, combat boots and a black, bedazzled T-shirt with supersized magenta, ruffled sleeves as she delivered power poses and pouts. Less than halfway through, the maturation that anchored the beginning of the show felt like a dream.

“I want you to have the best time tonight!” she said, addressing the crowd. “Whatever kind of day you had, just lose yourself in the music and have fun with us, alright?”

As country-tinged stomper “Here’s to Never Growing Up” rang out, it was as if Lavigne had turned back the years in a matter of minutes. “Complicated,” her breakthrough single, came just four songs into her 15-cut set, while new song “Warrior” was lost amid a run that included “Breakaway” (written by Lavigne, but made popular by Kelly Clarkson), “Keep Holding On” and “When You’re Gone.”

Though the theater proved a fitting venue for her singer-songwriter presentation, it, at times, felt like getting a peek at sound check — stop-and-go pacing continuing as bursts of choruses would dissolve into instrument tinkering, and other songs just simply ended. Lavigne never occupied the same seamless “pop machine” performance vein as her counterparts, where sequencing is used to tell a story, evoke suspense or drama. She instead opted for a much more straightforward approach to her live show. Thursday felt like a first attempt at something grander that was just out of reach.

In the middle of “Hello Kitty,” everything stopped. The LED screen displaying montages of music videos past and present, hot-pink skulls and stars in the night sky went black and the band stood silently on stage. The pause lasted barely two minutes, but it felt like 20.

But Lavigne, nearly two decades into her career, brought it home in the end. If you can suspend reality, her immortal teenager vibe is as infectious as ever and, despite everything, feels like the artist as her most authentic self. The one-two punch of the angsty “He Wasn’t” and buoyant, misogyny-lite “Sk8er Boi” probably would’ve given way to crowd surfing had the venue not been seats-only.

A two-song encore saved the best for last. After taking to the piano for “Fell in love with the Devil,” the soft sound of violin led into arguably the best song in her catalog, “I’m With You.” Her voice soared, slight yodel inflection echoing softly before being swallowed up by the thousands of voices singing back at her. While Avril Lavigne didn’t necessarily take her audience by the hand to take them somewhere new, they’re definitely still with her.