I'm not going to invite a girl I've been seeing over for christmas with my family
Why wouldn't you invite her if you are dating?
She is a bad influence on my family.
You should let your family judge her for themselves. She may not be such a bad influence as you may think.
I really hate her though. I really do not even enjoy spending time with her.
If this is how you feel, then you may want to end the relationship.  There is no sense in continuing something that will not go anywhere.