How would you deal with built up resentment?

I live with a flatmate. We knew each other before we started living together but were never friends. She is overall a nice person and a good flatmate, that is why my resentment is a problem. When we moved in together I didn’t establish clear boundaries between us. Because of this, she was constantly in my personal space. In addition to that, I got to know her much better and understood that we are definitely not compatible as friends. So the resentment started to build up. At some point I started to ignore her and we almost stopped talking completely. Right now she doesn’t talk that much and isn’t in my space all of the time. The thing is, even though I’m comfortable now the resentment hasn’t gone. I would say it stayed at the same level or even grew stronger. It got to the point that I can be in a good mood and it’s enough for her to say Hiii and my mind goes into Oh f**k off state.

Is there something I can do to change my attitude?