I need some advice for an awkward situation.?

Ok. So. My stepmom and I absolutely hate each others' guts. My dad and her aren't together anymore, but she ended up getting pregnant and having a baby girl named Khloe. Well, it might not be my dad's (but they haven't found out yet). Anyway, my dad wants me to stay at his house over easter holidays. But that means I'll have to go with him when he goes to see Khloe. I have nothing against Khloe, but I promised myself that I would never be in the same room with my stepmom ever again as long as I could help it. (The reason why requires a lot of backstory. The point is, every time I see her I want to squeeze her neck till she pops, and that will never change.) So what should I do? It's not like my dad can just leave me at home while he sees Khloe. What dad would leave his baby at home while he sees another that might not be his? I really want to spend the time with him over the holidays, but I won't be able to avoid my stepmom. It'll be an awkward situation, that's for sure. Help please! :) Thank yew!!