Don't sink to her level, but yes you should stick up for yourself.
My friend just did the same as she was getting abuse after abuse from her partners half sister.
Jealousy comes to mind because this girl was 'best friends' with my friends boyfriend, and because he's moved to the other side of the country to be with my friend, and apparently doesn't bother with his half sister, she's hit the roof! She even started bringing up petty little things, e.g. "*My friends name* all you did was wear your pajama's around the house when you were here, don't you think that's a little rude and lazy?".. My friend simply replied, "I felt comfortable to wear pajama's around my boyfriends family, sorry that offended you, and also I dressed up whenever we went out, but for the days we didn't go out, yes I did wear my pajama's as that is what I would do at home". My friend has now (like you) said to her OH, "You can go on the train and visit your family whenever you like, but I will not be going with you next time".
I can honestly say I have a great relationship with my OH's family.
Although his Mum doesn't really want us to have a baby, Which is what we both want.
Well done you for sticking up for yourself.
Hope things get better!