I found out after our date was selected and deposits paid that our wedding date is my FSIL's anniversary. My future husband and his sister are not close and I have never actually met her as she lives out of state. I was speaking with his mother and she told me that his sister is very upset that we are having OUR wedding on HER anniversary. I had no idea it was her anniversary when I set the date. My future husband did attend her wedding but the date did not ring a bell to him in the planning as it was several years ago. Any advice for approaching this situation?