What do you do when you have to be around people u dont like?

I dont get along with my BIL's wife and being as the in-laws are such a close family I will have to be around her often (Especially as we will be staying there with them for 9 days next week). I just REALLY dont get along with her. But I dont want to deliberately avoid her at all costs and then cause some kind of rift within the family. How do you cope with people you dont like but you have to be around?