Sounds like quite an evening…sorry things are rough. One question...I can't remember if you said...is Dot spayed?
One thing to do is really observe her and her interaction with Otis - is there some sort of eye contact or body language thing going on that you haven't picked up on. It could even be Otis shooting her a glance of some sort that is setting her off - or not. If you pick up on it, you can end it before it escalates. But you really have to watch to see the signs.
An example of what I mean...
When Brando first got injured - there was a lot of bad glances going on between Ruby and Brando - and you could feel the tension in their energy. You could tell that Ruby was waiting to jump Brando, and it was up to me to make sure that didn't happen as he was injured and needed my protection. I think I said it before, but it ended up that I needed to separate the two of them for 6 weeks.
Even though the energy was pretty much back to normal when he got his cast off and I re-introduced them, at first Ruby would still try to set up Brando to jump him - and I could tell it by watching the way she moved around him, the eye contact she made or tried to make, or her interaction with him when he was playing with Aaliyah. Thru redirection and inserting myself in the middle of the play to stop it when I could see the signs that it could go off the rails, Ruby has stopped the behavior and the pack is back to normal - in fact, I think better than before as Ruby seems more stable. I would say that any sort of trouble between Ruby and Brando never came without warning - it was just whether I was proactive and picked up on the warning signs and did anything about them. I do now. And if I couldn't watch them, I couldn't leave them in the same room together and trust that nothing would happen.
It sounds like you might need to separate them while in the house. In my house, they could still see each other, but they couldn't get to each other.
Pat had a good suggestion about contacting Sharron - I'm sure she's seen it all in fostering. I would also highly recommend 2 little books by Patricia McConnell - How to Be the Leader of the Pack and Feisty Fido. They are short reads, but have great advice.