Why would an EX message me after I dumped her?

The story goes like this. She was complaining all the time. By the way, she wasn't like this before. When we started, for the first 2-3 years, she was quite good but later started complaining and before that I never used to care but later she asked me if I can emotionally support her during the issues and although I didn't cared her much, I started caring more than before. This kind of made me negative later on because I couldn't take all the negativity anymore. So there were fights and arguments and then later, I became like the old me who wouldn't really care anything.

The arguments were increasing. Her nephew died, her family had so many issues and she wanted to live with them all on a sudden. So I broke up with her. I messaged her after a week or so for a help(We are both same professionals) and it was nothing related to our relationship yet she started saying things like " I am over you" , "We are done" and "You treated me like a doormat" and so on. She was so rude so naturally she is not really rude although she complains a lot. So I basically said, I don't think we have to be rude to each other and we can be positive. When I said that, she even make fun of me calling me a millionaire and stating that I don't care the poor.

That night we talked a lot and I explained why we can break up being a bit positive. I usually would not have talked but her negativity, rudeness and meanness caught be off the guard. I couldn't believe its her. Also, I was drunk. Anyway, the next day I woke up and thought that I'd never contact this person like ever.

The next day, she messaged me asking me if I am fine and "We can be friends" and "Do you hate me" and "Do you have a grudge on me".

This doesn't make sense. Now funnily enough, my best friend also broke up the same and his girl acted the same. We don't know each other. Do girls do this all the time?

Why is she doing this?