Um, this family dynamic sounds absolutely disastrous. Like, we're talking right out of one of those painful reality shows. What kind of person has the audacity to steal their sibling's partner, marry them, and then throw a temper tantrum when their sibling doesn't want to attend the wedding? What did she expect? It sounds like someone's grown very comfortable living in their own little fantasy world. Yes, a fantasy world where she's blinded by such a thick haze of self-concerned narcissism that she's completely detached herself from her moral compass.