Dealing with Sister in Law

[Nickyd1228]

I am getting married in July and I have had porblems with my soon to be sister in law everysince my fiance and I began to get close. Whenever she needs anything we are there for her, she has stayed with us(her, her husband, and her three children), we have given her money and havent gotten it back. She has threatened me on numerous occasions and now is saying that she doesn't want to be a part of our wedding. I really don't want any violence to come into the picture so what do I do?