Keith and I call each other lots of names but all done in a joking way/matter. We both know that nothing we ever say (such names) are serious or meant to be true.

It depends on what her and your moods were when you both had that conversation. There are times that Keith has offended me when he said something while we are having a serious argument. But we always patch things up afterwards. Did you apologise when you found out it offended her? How long before you found out? Coz that would make a difference especially for a sensitive person.