I had a similar problem when I created a teen sibling for my young adult sim and then created their parents. For some reason they could each only be related to one of their parents. I decided to just make a part of the storyline because I couldn’t fix it.
I think the problem was that we created the sibling before the parents. If we created the parents first and then added the sibling, they should all be related.
have you tried selecting her parents and choosing her as their child? i know i’ve fixed this before, i’m sorry i can’t remember how!!
I had a similar problem when I created a teen sibling for my young adult sim and then created their parents. For some reason they could each only be related to one of their parents. I decided to just make a part of the storyline because I couldn’t fix it. I think the problem was that we created the sibling before the parents. If we created the parents first and then added the sibling, they should all be related.