Annie,

I don’t think it’s wrong that you want to be selective in who you choose to be around you. I however think you might be pushing the limitations by trying to get your BF to assert to his sister to stay away from you. Its unfortunate, but you really cannot choose who your BF is connected to. Have you considered speaking to the sister? Maybe with a mediator (like your BF or his parents) and just hash out what the hell is going on. Because, it could simply be that (as you stated above) that she is just jealous and taking it out on you. This could just be because your the first one in the firing line. Whether it’s realistic or not for your BF to exclude his sister comes down to his choice. I believe that Anita also states to try speaking to your BF and not ‘make’ him understand, but try to convey your feelings on his sister.

Another logical conclusion, something which you could do, is simply ignore her. I know in the confines of a house, especially her family home, this is difficult. But having a strong mind against her weak insults may be better for the time being, rather than letting her get to you. I mean, you know ‘why’ she is doing it, and well it’s her own fault if she cannot get her act together. I know that it’s the principle that matters, you shouldn’t have to deal with this, but these are the cards that have been dealt. By no means should you accept the result, but her problem seems to be targeted at you, not her family. If her parents are embarrassed by her performance, then i would be making them aware of how she makes you feel. They might not (as you wrote) find it abusive, because they have lived with it for years. So try to impart that too to your BF, that what your BF and parents are feeling is based on previous experiences, which is not how you see it.

I hope this helps in some way, i feel you understand why she is doing this, but it still hurts no matter the whys. At some point you are going to have to speak to her, maybe even in a ‘teacher/ student’ kind of way. Because although you are not her family, she may become apart of yours.
MAtty