Problem with the in-laws

For whatever reason, my sister-in-law to be hates me. See, I'm an introvert and can be very quiet and reserved when I'm around people. But, when I get comfortable with a person, I crack jokes about the person. I never try to be mean, but I guess she saw it as a slight against her. So, the next few times I saw her, I kept to myself and only talked to her when she talked to me. The last time we interacted was at her house. My fiancee and I had been traveling all day and I just wanted to go home, but she wanted to see her sister's new baby. So we went over, and I didn't talk much, just sat in the living room until my fiancee was done visiting with the baby and her sister. The next day, my fiancee gets a text from her sister saying it was disrespectful that I didn't talk that much to her and her husband and that I didn't shake her husband's hand when I entered the house. She also stated that my fiancee should apologize for my actions and if she didn't, my sister-in-law to be wouldn't take part in our wedding. I've been to her house multiple times and this is the first time she mentions the hand shaking thing. And I know my quietness can be seen as disrespectful, but that is just who I am. My fiancee says her sister is a bully and a crappy person and only does these things because she can and probably won't back down from this until she gets her way. Sorry for the long post, but for those that did read it, any advice?