Please use this thread going forward: [CHEAT] Cannot edit pre-existing sims | EA Forums - 11924857
I think its because the mother has a sister. If you make siblings with no parents the game makes a dummy parent to make that relationship (you can see it in the family tree in game). You can then set a second parent later (the mother in your case) but then adding the father would be a third parent, which the game doesn't allow. you can use cheats ("testingcheats true" and then "cas.fulleditmode") which will allow you to edit the family as if you just made it in CAS
in the sims family tree, she has only one parent - mother, and a step father (bizarre she could also be partnered to the step father)
Sister shows correctly linked only to the mother.
There is no unknown icon for her father.
However, her child has correct grandmother but unknown grandfather.
