Hi -
Well, you're not giving much to work with here...
I've never heard of IER (not that that means a whole lot) but I don't think that the two are necessarly tied. PTSD plays into many many things. But I think you're gonna have to talk with a professional about these questions. There are too many blanks.

Sexual abuse of other is all about CHOICE. Choosing to hurt others. End of story. You are not saying who the father is... nor who the daughter is. If you are the father, or know the father as a friend, try to get help for that person. There is counseling for abusers and programs to help.

If you are the daughter, find someone safe to tell and get help.

Regardless of who you are - hurting another is never ok, never justifed. If you think you will hurt someone, get help.