Tell her this "I feel like you want to tell me something, but you're not saying it. What is it? Your behavior towards me hasn't been usual." If she says she wants to be your girlfriend, just tell her that you're not interested. If you're just trying to avoid her, she will keep trying until she succeeds. When she realizes that she won't have anything with you, she will only feel worse for having wasted her time. It's better to be direct rather than indifferent.