I'm not going to get my sister a christmas gift
Why are you thinking of not gifting her?
My parents are paying for her present
Just because your parents are getting her a gift doesn't mean you don't have to.  Family members are expected to exchange gifts over the holidays.  How would you feel if she didn't get you a present?
It will be just fine, I don't really like her and I can't think of anything good.
I think that if you can afford it, the nice thing to do would be to get her a gift. I think that it is almost tradition that families exchange gifts during the holidays.