I am assuming you are using a newer version of FTM.

Under the Person tab for the wife, the one between View and Tools, select Attach/Detach and Detach Selected Person. This will bring up a list of all the families she is attached to. She should be attached to her husband and to her parents. I suspect you will also find she is attached to her husband’s parents. If so, detach her from this family.

Curt