I want my mom to talk to my girlfriend
Is there an issue between the two of them?
Yes. She doesn't like my mom and I think they need to talk
Wanting them to talk about their issues is admirable. People in your life should be encouraged to get along with each other, and to resolve problems peacefully.
They will talk, I just have to find a way to make my mom accept her
It was good of you to try to get them to talk this out calmly and peacefully. There may be some lingering resentment toward your girlfriend by your mother, but this is probably just her trying to look out for you. I'm sure that as your relationship develops, your mother will grow more accepting.