My sim has disappeared!

The daughter of one of my families has disappeared! :(
I switched over to play another household for a little bit and then when I went back to my other family the daughter has suddenly gone!
I am able to invite her over but I wasn't able to ask her to move in and I cannot find out where she has gone. I couldn't find her in any of the households under 'manage households' either. Is there any way to get her back? :(