I don’t get it

I used to be really good friends with this girl. She helped me through my first heart break and everything. Then we just stopped talking. At school one day I was low key crying because my ex bf did something and she came up to me and talked to me. And then we stopped talking again and eventually I said hi to her at a basketball game and she just says “hey” but in a rude way and kept walking. Over text I asked her if she was mad at me and she said “no why would you think that”?

This was all like 2 months ago and today I noticed she unadded me on snap chat. I have no idea what I possibly could have done to make her not like me. There’s not one single thing I could have done that would have hurt her. Nothing. I just don’t understand and it’s making me kind of sad. Has anyone been through this? What should I do ?

Idk what category to put this under