What's the deal with her always being shy around me?

I've had a crush on her for like 7 months at first I was shy around her I would it make super highkey that I like her I told everybody even her and she wasn't shy at first cuz she didn't like me(she's not a shy person at all she was never shy with any other crushes or even with her ex's) but now she's super shy around me,she rejected me but she didnt even look at me she was staring at the floor, I was cool with it, then a week or two later she asked me out and I told her no since i didn't know if she was serious or not. Everytime I see her she avoids me, last time she left her class and I happen to be passin through and she saw me and she goes back in the classroom. In PE I would always be sitting on the bench with my friends and the bench was infront of the locker room and she would never come out until I left. Whenever we had a class presentation she would always hide so I couldnt see her, we dated for a week but It took so long to date her that I lost feelings for her. It's been two months since I saw/broke up with her and yesterday I saw her. I'm best friends with her female best friend and she invited us and 2 other people to hang out with her. She was sitting on the table with my friend and I guess she wasnt expecting to see me cuz when I got there she turned around and kept looking the other way, when we were walking she was on the other side of me. We were on a roller coaster and I sat next to her, she looked really tense. but yeah, why is she so shy around me?