I have a similar story. After I got married to my husband (we had been engaged for 6 months and dated for almost two years) his sister announced that I am doing it all for the green card. It didn't end there, she said that she thinks that I am gathering and falsifying evidence to report him to the police in attempt to inprison him. Also that I am cheating on him with MULTIPLE other guys. Well, two years later, she has not acknowledged how bad shit crazy that was nor has she apologized. 

The whole thing continues to have a horrible effect. I have no relationships with his family, besides exchanging forced pleasantries once or twice a year.