I'm not going to come over to help my gf with the cops
What will you do instead?
I will wait outside her house for the cops to arrive.
A relationship is based on trust and support for each other. Being there for her while she's dealing with an authority figure will help her get through the situation easier.
She's a liar and I hate her guts. I'm not going to be there for her when they come arrest her.
It can be hard to be there for someone when they have not treated you well but if you are still in a relationship, you should be there for her. Being arrested is stressful and she needs you there at this time.