My FI and I have been together for three years. I am friendly with his family but not close. It is pretty clear, though, that his only sister does not like me, and FI has confirmed this. She doesn't really speak to me when she visits. Every time I try to talk to her she shuts the conversations down as soon as possible. When she does respond to me it is to contradict me, and her demeanor is just kind of hostile. It makes me uncomfortable. Neither FI nor I know the reason, other than that he moved several states away to be with me.
Our engagement isn't public yet, and I'm hoping that she'll just get over it. But I have my own family experience with long-running hostility and conflict, and I know you have to be super political sometimes to get along. With that in mind, I'm trying to make sure I don't do anything in wedding planning/activities that could deepen her resentment or make her complain to her family. I'll ask her to be in the wedding party with a nice email (FI did not want her in his wedding party and it wouldn't fly for me to exclude her). I'm buying the dresses (I'll make sure she approves her dress). Aside from attending the wedding, I won't make any demands on her time or money. She will be invited to the shower and bachelorette weekend, and I'm going to distance myself from those invites to make sure she can't object to any excesses. I think the chance of her attending either is less than zero.
My question is whether there is anything unexpected that causes conflict that I should be thinking of? Does anyone have experience getting blindsided by pouty family members?