Sister-in-Law driving me crazy...advice?

She doesn't sound like a nice person to begin with, plus she is jealous of you. It's possible that its because you are 6 years younger and getting married, and she is (I am uming) single? I know it's hard to say something when you are a non confrontational person, but she is walking all over you. The best thing to say to her when she says something snarky is simply "why would you say that?" especially in front of others. She will be the one who is embarred. And if your fiance is present, he could ask her that as well. She won't like being put on the spot by her brother. You should talk to him about what is going on. Next time you see her, just be prepared to say something back to her, but do it very nicely. Kill her with kindness, even though shes not doing the same for you. Good luck!