I'm hoping my girlfriend's mom dies pretty soon.
Why would you wish death on your girlfriend's mom?
I'm tired of thinking about her and I want her to go away.
It's very common to not have great relationships with your partner's parents. But, that is no reason to wish death upon them. If your girlfriend hears you say this, she will be very sad and disappointed in you. You should think about how she would feel about the loss of a parent.
I don't care since I'm going to break up with her.
If you are planning on breaking up with your girlfriend than I do not really see the reason why you want her mom to die. If you would rather have her mom out of your life, you should simply break up with your girlfriend now.