Got rejected 3 months ago, she now comes back and said she made a mistake. What would you do?

There was this girl I really liked, we never really talked that much only a couple times since I didn't really have any interest in her yet. After a couple months she wouldn't even want to talk to me instead she would just stare at me, as if 'seeking validation or something'. She gave me clear signs like checking me out, even my friends noticed that she gazed me up and down and blushed. To be honest I'm not sure if she's shy, it's like she has different personalities really weird My friend would notice that she spoke to people differently. Anyway, we never really talked that much and I could never ever close that gap of communication. After a couple months I asked whether she wanted to hangout at school and perhaps talk ( this was via text because I couldn't get her to talk in real life). Another odd thing is that we had this final shirt signing day, I signed her shirt but when I asked her to sign mine, she just says, "Maybe tomorrow." I just said alright, after that she just keeps starring at me from a distance (Never signed the shirt by the way). She rejected me via text saying she 'has someone else' which is extremely hard to believe because she normally talks to her female friends. it took me awhile to get over the rejected but after 3 months she, texts me and stays, "Hey I'm really sorry. I made a mistake." To be honest, I don't believe she has the maturity or integrity to be in any relationships. One of my friends who knew her said that she was a 'bitch' and 'insecure'. What do you think is up with her and what would you do?
Got rejected 3 months ago, she now comes back and said she made a mistake. What would you do?
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