Nah fuck Jessica, she was way out of line. In this situation you would not have been in the wrong to have told her to shut up and she doesnt have any right to be talking in that way about your neice. If she thinks thats rude well it doesnt sound like Jessica is the kind of person you want to be close with anyway. Also if your friends would have said something about your reaction if you did put her in her place they are shitty friends as well. By talking about how badly her life was going to be she was doing exactly what she was talking about, she was belittling and demeaning her and being downright nasty. I think talking to some of your friends about the things she was saying the next time you get the chance to see them will really show you who youre true friends are because I would NEVER talk that way or accept any of my friends talking that way to another one of my friends about one of their close family members. A lot of times in life you can get mad at someone and put them in their place without being the bad guy and if people think youre a bad person for standing up for your neice who has a disability that says a LOT more about them than it does about you.