Hello!
Well, it really depends on if you can go on thinking about what you could've had or if you really want to do something about it and find out! I don't know if she likes you or not from just what I've read. Every women act differently when they like someone. I've known women who purposely not pay much attention to someone they were attracted to hoping that the person they are attracted to will approach her first.

What should you say to her? Anything. Keep it simple at first. Say hello. Think of something to say to make her smile. Develop a friendship first. You will know by how she responds if she is interested in getting to know you better.