This girl is a woman now.

Though Avril Lavinge just left her teen years in September, it would take considerably more than a chronological point of reference to leave her trademark do-it-my-way spirit behind. It’s still very much in evident in the first of her 20Something years.

That’s a birthday present the Canadian artist continues to give to herself as she opens a new chapter of her life and career. The previous one (becoming, at 17, one of music’s top-selling artists, selling 14 million copies of her 2002 debut CD, "Let Go," earning eight Grammy nominations) has proven to be an exciting "read" for her and fans worldwide who identified not just with her accessible rock but also its message of independence.

In another era, Australian pop singer Helen Reddy proudly proclaimed, "I Am Woman (Hear Me Roar)," in her Grammy-winning 1972 song.

Though stylistically in another musical world, and with an in-your-face attitude that Reddy probably would have blushed in attempting, Lavigne essentially is delivering the same proclamation for a new generation.

"It’s been a pleasant surprise," she says, in classic understatement, as she looks back on her own road less traveled. "It’s gone very well. I guess I never thought about what it would do, especially coming out with the first record."

"Let Go" was the third biggest-selling album of 2002, propelled by such singles as "Complicated."

She senses she is on to new adventures, she adds in a morning conversation from Belfast. "Yes, I definitely do. I’m starting my tour. I feel like I’ve stepped up a notch performing. I perform three songs on piano and three songs by myself on acoustic guitar in my shows," she explains.

And then there’s her new album, "Under My Skin," which as of September had already sold more than five million copies worldwide, in which she took charge in a significant way. "I took a lot more control," she says. It is work that she believes represents growth for her. That in part comes from the maturation process, heightened undoubtedly by the fishbowl existence which, for better or worse, seems to be the byproduct these days of such intriguing success.

Returning from her world tour, unbeknownst to her management or record label, she got together with Chantal Kreviazuk, her fellow Canadian singer-songwriter, and they co-wrote 12 songs. Lavigne moved into the California home shared by Kreviazuk and her producer-husband Raine Maida (of Our Lady Peace) and began recording.

The unaltered results comprise the bulk of "Under My Skin." The artist cut the remainder of the songs nearby, co-written with her guitarist Evan Taubenfeld, and one track with former Evanescence guitarist Ben Moody.

Lavigne speaks with pride of having been involved with every aspect of making this record – from the sound of the drums to the guitar tones. She admits to being "really picky" with her sound now that she understands the process so much better.

She insists it is not difficult to maintain control of her own career, even in these still early stages. "I work closely with my management. Everything goes through me. I’m very particular about everything," she says.

When others know that you know what you are doing, it is not hard to win respect she implies. "I might say, ‘I don’t like something that way.’ They have learned very quickly," she says. "It didn’t take very long," she adds, laughing. "They know I know what I want. Everything is awesome."

The view from inside the industry is decidedly different than when you are on the outside looking in, she suggests. "What you don’t understand before you get into it is that you really put yourself out there," she explains. "The more popular you get the more people talk about you, even making things up. Some people are really judgmental."

No one really knows unless they are in it how harsh it can be, either, she says. "It’s very harsh. And seeing how the business really works, some people really don’t care about the music, business people. They care about other things."

You just have to be careful about who you work with, she says. "I’ve been really fortunate. I’ve got good people around me who care about me."

Lavigne, who in addition to her nomination for an American Music Award for "favorite female artist" in pop-rock also has received the World Music Award for "pop rock artist," believes people care about her music because it comes from personal experience.

"People can relate to that and I’m glad," she says. "I’ve got a lot of fan mail. People talk about why songs touched them. It’s very rewarding to me," she adds.

She sees her new album as more serious in certain ways.

"Slipped Away" is a tribute to her grandfather who died while she was touring. She says it was the first death that she had experienced. "Together" explores the delicate territory of knowing when to admit to yourself that a relationship is not working. "Don’t Tell Me" is what she calls her "girl power" song, a reminder to her female fans not to let themselves be pressured into intimacy if they don’t feel it is right.

"Who Knows" and "Take Me Away" reflect welcome optimism.

Time Magazine praised Lavigne’s "My Happy Ending," the second single off "Under My Skin," as one of 2004’s "12 Songs of Summer." One reviewer called it a "mini-empowerment anthem."

Lavigne’s music touches both youth and adults. It’s not lost on her that she is viewed in some circles as a role model.

She appreciates that, she implies, but does not let that affect her. "It doesn’t make me self conscious. I don’t worry about my actions or what I say," she insists. "I’m a role model for what I’ve always been: a person outspoken about what’s on my mind, being honest and real. I think that’s a good thing."

She hopes younger girls learn from that. "I hope they see, ‘She is herself and does what she wants and stands up for herself.’ I think it’s good for other people to be like that."

No mystery surrounds what motivates her. "It’s fun," Lavigne says. "I’m on tour and this is a blast. I’m totally motivated. I love music, performing, playing my instrument, being on stage and trying to be the best I can. I’m hard on myself. After a show, I have all these notes. I ask myself, ‘What can I do to make the show better.’ I walk around with my notes and talk to the light man, the soundman and others. They say, ‘Here she comes again,’ but I can’t help it though."

She has enjoyed her move to playing arenas. "I love it. Of course there are so many people. That’s very exciting going, ‘My gosh, all these people up here seeing me!’ That’s very cool."

It is more challenging trying to connect with an audience or getting the sound you want in larger venues, she acknowledges. "I just work harder doing that, connecting with them. I put as much into it as I can."

She is finding that European audiences react differently overall to her music.

"I don’t know what it is, it’s just kind of everyone is more like crazy. If you just walk out on the street they start screaming. And you have a million letters sent to you. In America you get that, but not as much. In Europe, they seem more excitable over here. Maybe it’s because I’m not here very often."

Or maybe it’s the all-encompassing girl/now-woman power of Avril Lavigne.

As Lavigne herself says, "Music is a very wonderful thing."