Sounds like your mom doesn't want to lose her baby. I don't see anything (from what you have written) that would give your mom and honest reason to dislike your girlfriend and I saw in your profile that you are 19 which makes me think your mom is more so upset that she is losing her baby! Are you the youngest? If so, then I'd say that is hitting the nail on the head.

The girlfriend however, why would she like your mom that doesn't even want her in her house? I don't like my bf's dad but who cares. We are in this relationship - not them. If you can find someone who loves your family, you and you love her AND her family.....well you are damn lucky. I'm not sure I know one couple who doesn't have at least something bad to say about some member of the family.

Talk to your mom. Tell her you understand her concern but that you are an adult and able to make your own decisions. If she won't listen then it may be time to have a talk with your gf about coming up with ways to avoid the situation.

One last question....do you live at home with your mom? If so.....then it is her house and, if she doesn't want her there, that's her choice. That's why I moved out so young. I was broke as a joke but I could do whatever I wanted without having to listen to my parents lol