Thank you so much for rescuing this kitty!
There are some things you can try to help calm a multi-cat household.
Flower essences: http://www.petsynergy.com/flower.html
You can also try Feliway - the spray or the plug-ins for rooms (or a combination of both): http://www.catfaeries.com/feliway.html
You could call around to vets or search on line to see if you can find a cat behaviorist in your area.
The only other thing I can think of off hand is that she wasn't confined to her own room long enough. You may want to consider starting over. If you have a guest room that can be "hers," consider putting on a screen door. This will help your existing kitties feel safe in "their" territory again. It will help your rescue feel safe in hers. And they can get used to each other (again) - but in a non-threatening situation for any of them.
For helping feral cats become used to other cats in the home, one of the tricks is to put the kitty in a large crate in the middle of like your living room - with the crate covered with something light at first, leaving one side open and having a box in there so there's a place to hide.
Being able to observe the other kitties, she may learn from watching them interact.
We rescued a kitten born with brain damage (also caused physical damage). She never learned "cat language" before she came home with us. She violated everyone's space, totally ignored their body language, and it was chaos for a while. Two years later, she has completely learned their "language," and participates in the gang like a normal kitty. Of course there's still the usual tiff at times - but that's to be expected in a multi cat home. The difference here is that she couldn't intimidate anyone much, because the problem also left her physically handicapped.
You can also try rubbing the little girl all over with a hand towl. Put treats out for new 7-year old. Rub new 7-year old all over with a hand towl (or rag or whatever), and put treats out for little girl on this. Do this 1 to 2 times a day at regular times. This will help them come to associate each others' smell with good things. It certainly can't hurt and may help. Especially if you start over by having 7 year old in a room by herself. Though if you do decide to do this, just make sure that you and the family spend as much time in there as possible - doing whatever you can find to do in there. Don't want her to feel abandoned and punished.
Just ideas. I hope they may help.