Honestly, I'd ask her straight. Why did she sign up for a mentor? What does she hope to get out of this experience? Seriously, I would, I'd just say, "Hey. I notice that there seems to be a disconnect here, (insert above questions)." See where that goes, if she continues to be non-responsive (and kinda rude, honestly), I'd speak to the teacher or whomever it is that coordinates this program.