My friend keeps mockingly repeating whatever I say

I don’t know if this is the adequate place to post this, but my friend won’t stop mockingly repeating what I say as if I’m dumb?? She doesn’t only do this to me but she primarily does it with me. It’s really starting to annoy me because I don’t get why she does this. For example she will ask a question because she needs help and even when I give her a genuinely useful answer, she will say it back to me mockingly. She’s also the type of person to “tease” her friends by insulting them and most of the time it doesn’t bother me, but she does it CONSTANTLY. I really don’t enjoy calling people annoying but idk how to make her realize that i really don’t appreciate her behavior at all. She’s also kinda selfish but expects others to give her things and do her favors. For example, I always accompany her to buy a meal even when I already have something to eat, but she won’t do the same for me. Also whenever I talk she goes quiet and it’s like she’s not even listening to me. After I’m done talking she will wait a few seconds and then switch topics.

I really don’t know what to do because she’s really not all that bad, but this side of her is just awful to bear. It’s like she’s sucking the energy out of me.