Sister in law rant

I know this isn't pregnancy related (exactly), but my I swear my sister in law is trying to ruin my relationship with my mother in law. I am 26 weeks pregnant and my sister in law is always trying to start some drama. I have always let it go and tried to be the bigger person. Maybe it's the pregnancy hormones but I just can't seem to let this go. She is being a nasty mean B. Trying to start drama with my MIL and it's turned into a "he said, she said". I can't stand it. I feel like she is jealous that she isn't the only "daughter" in the family and her kids won't be the only grandkids come March. I don't know what to do with her. Ugh!