When you are on her profile page, click the EDIT tab from the tabs across the top.
On the right hand side, the list of family members like father/mother/spouse etc. each has an (edit) button or and (add/edit) button. Click on the relationship you want to disconnect.
On the page that comes up, scroll down and check the relationship you wish to Remove, and save the page.
Then you can go back to the EDIT page, and using the same buttons, connect her to the correct relationship.