What is it when someone quickly looks away when you approach? Was she just shy/nervous?

I have always found that when someone is watching me it is best to approach them if you are into them. Next time go up and ask how her day is going and try to make it light hearted and not awkward. If she does like you it will give her hope again, but then it is up to you to make the moves. She does sound shy so try and make her feel like a friend and comfortable. It will help :)