I want to ask you, is this okay to feel like I should cut off my girlfriend's mom from my life?
Oh wow! I am not sure I know why? I am almost in shock here, really you want this?
She doesn't like me at all and she has insulted me countless times.
I'm sorry that is how you are feeling. Partners are expected to get along with each other's family. If your girlfriend is going to be in your life for a long time, you need to find a way to get along with her family.
Since she always fights with me, I don't need her in my life for anything.
I know getting along with in-laws is not always so easy. Sit down calmly one day when you are both ready and be civil, make jokes, make her laugh and be a friendly guy. I think you could win her heart over eventually.