I don’t use Risperdal because of the increased risk of neurological side-effects, and increased prolactin interfering with hormones, including estrogen. Lexapro is good for anxiety, obsessiveness, and depression, especially sadness, but if your daughter is manic depressed/bipolar the Lexapro can make her more emotionally unstable. Effexor XR is a broader spectrum medication with potential advantages but would also destabilize if she is bipolar.
How thorough was her examination? What family history is there for anxiety, depression, or bipolar?
If your daughter needs a mood stabilizer or something to "glue" her thoughts I have had the best luck with Abilify or Seroquel. test.askdrjones.com/2005/02/14/ranking-the-mood-stabilizers/
Age fifteen is such a critical time developmentally so you need an experienced clinician and you need to be seeing some improvement.