Testingcheats and cas.fulleditmode isn't working?

So I have testingcheats true and cas.fulleditmode true as well but when I go to edit a sim and make her the mother of my simself's daughter it won't let me change the relationship so the new sim will be the mom

Am I doing something wrong? Should I just replace the daughter with herself from the gallery and delete the other and get her relationships up again?