Why is she doing this?

I’m in high school and this girl likes me and where talking but I said your not my gf. And I don’t know if she’s trying to pull jealousy stunts or what but it’s really annoying me and pissing me off. Recently she’s been saying I’m mean to her and this is why tbh but she still does what I want her to do she’s nice and helps me and does stuff for me. But she is doing things like in class she will be talking to her friend right next to me about other guys like she will say one is cute and he slid in her dms. And talk highly about him and when I ask she says it nothing.

Then she will just do thotty stuff like act real friendly to other guys in front of me or when I’m around. And when I asked why she couldn’t come over she said I was out late last night and was vague and I asked if she was sucking D as a joke and she gave a fake laugh and changed the subject. And she will intentionally scroll through her iPhone messages. And also she will say to her gf in class this guy made a move on me and the biggest one we got into a play fight and I said give me a kiss and to make up she said no and then the next day she said she finally kissed “him” this really pissed me off. Idk why she would do this. Can you help me understand why she does this.