Why wouldn't you know if your daughter was abused? Were you and her father together when she was a child? Was he violent or of the abusive type? Could she have been sexually abused? Are you sure she never said anything about being abused, or touched?
Did she ever draw strange pictures that made you wonder what was going on?
Try thinking back. Maybe something will pop up in your head.

Although I hope not.
God bless & take care. Hugs, Lee