In the last few minutes of the season-two finale, Rue says she stays clean for the rest of her junior year. She seems to have gotten herself on the right path, and hopefully it stays that way in season three. But even Rue seems somewhat doubtful about whether she can maintain her sobriety. "I wish I could say [staying clean] was a decision I made," she says in her season-ending monologue. "In some ways, it was just easier. I don't know if this feeling will last forever, but I'm trying."
This is a show that centres pretty heavily on drug use, so while we want Rue to stay clean, we wouldn't be surprised if things take a turn again. Still, if Rue stays away from toxic people, she might have a better chance of staying clean. Lexi is definitely a good influence, whereas Elliot certainly isn't.