What happened to "Winnie?"

Former "Wonder Years" star DANICA MCKELLAR kissed a girl — and she liked it!

The 38-year-old actress, who played brainy "Winnie" in the late '80s-early '90s TV hit, is so desperate to shed her good-girl image, she's locking lips with rocker AVRIL LAVIGNE in the singer's new "Rock N Roll" video.

"Danica's frustrated because no matter what she does, she can't seem to shake this image people have of her as squeaky-clean Winnie," said a source. "And, believe me, she's tried."

Danica eve appeared in a sexy photo shoot for "Stuff" magazine in July 2005 after the publication's readers voted her the '90s star they would most like to see in lingerie. She explained that she agreed to the shoot in part to obtain "grittier roles."

"But people still see her as a goody two-shoes," said the source. That's partly because the UCLA grad is a math whiz who's written several kids' books about math, including "Math Doesn't Suck" and "Kiss My Math."

The insider told The ENQUIRER: "Danica complained to a pal, 'I'm proud of being a bit of a nerd but I'm so much more than that!'"

Most of the jobs the actress gets offered these days are TV guest roles, low-budget movies and cartoon voice-over work.

"It all pays the bills but she's a divorced, single mom," said the source. Danica's son, Draco, is 3.

Danica, who played FRED SAVAGE's young love on "The Wonder Years," split with her husband of three years, musician Mike Verta, last year.

Now Danica's hoping that getting down and dirty with Avril will finally help producers see she's capable of handling racier roles with bigger paychecks.

Avril, 28, admitted it was the first girl-girl kiss for both her and Winnie.

"We never really talked about it afterward," she said. "But I think about the events of that day again and again, and somehow I know that Winnie does too."