Tween Twilight fans may have fueled the intense interest in New Moon star Kristen Stewart, but they’re going to be locked out of the actress’s next films: the R-rated The Runaways, the Joan Jett-Cherie Currie biopic with her New Moon costar Dakota Fanning (due in theaters March 19), and Welcome to the Rileys, which both screened at the Sundance Film Festival recently.

At the film fest in Park City, Utah, the 19-year-old wore skinny jeans and sneakers in the snow and a khaki jacket she pulled close against the endless cold. She had that rebel without a cause vibe, a junior James Dean. This was not an actress racing toward couture and acclaim, but nervously holding herself together, knees thrumming uncontrollably, until she could slip behind her next part.

As the 70’s rock rebel Joan Jett, Stewart channels the teen spirit of girls growing up in a world where pudgy guitar teachers unapologetically told them they couldn’t play electric guitar simply because they were girls. As Jett, she also takes drugs, blows pot smoke into the mouth of her bandmate Cherie Currie (Fanning) and plants a same-sex kiss. Bye-bye, Bella: Twilight this is not.

In Welcome to the Rileys Stewart plays a low-rent teen stripper who turns tricks for cash in New Orleans.The story? This runaway becomes the catalyst for parents (Oscar nominee Melissa Leo and The Sopranos star James Gandolfini) grieving over their daughter’s accidental death. It’s the kind of part that seems like a rite of passage for child stars stepping into adulthood. The actress is believable as yet another waif who would be luckier to make choices between a vampire and a wolfman, than the johns that walk in off Bourbon Street.

While these R-rated parts may not be quite the role models for which most moms would have asked, Stewart’s eclectic choice of roles, and ability to meet their demands, is a preface to what will likely be a long and prolific career in front of the camera. Is she ready for the challenge?