How long ago did your daughter move back home? You should give both dogs a little time to adjust to the new situation before introducing them to each other. It's too much too soon to bring them together when there is so much new stuff going on. If they are both or just one of them is unaltered, that too could cause problems which altering them both would help. Not all dogs will get along, so yes, they may have to always be separated. I have to do it with some of my dogs because that's mainly what I have is Pit Bulls and they would rather be with a person than another dog. I live with my mom and Ginger stays in my room with me since that's where I spend most of my time. If they still don't get along after a proper introduction, then the best thing to do is keep them separated for their own safety and yours. It's ok, they won't be upset if they don't get to play with each other as long as they get their own time alone with each of you and their regular routine continues as best as possible. Here are some links to help you with this situation:

http://www.pbrc.net/fightinfo.html

http://www.pbrc.net/rotate.html

I also encourage you to check out the rest of that site so you can get a better understanding of the Pit Bull breed. And welcome to Pet Talk.