where should reintroduction happen?

hi- i was hoping to get some further advice. We had a pretty severe incident of redirected aggression about a week ago from our older cat, cassidy, and my other cat(billie), myself and my husband were all targets(the cause was a weird noise in a movie we were watching) So Cassidy was kept in a separate room- we used feliway spray, and rescue remedy with her- and she is completely fine with us. we let her out at least once a day, while billie is in another room, to let her adjust to the apartment(she is still quite skittish out there) We also have been letting billie smell cassidy through a crack in the door- and neither cat has a reaction (tail, ears normal, no hissing, no growling) BIllie is a lot smaller and really has no ability to fight back- she is just confused and tried to run away when cassidy attacked

i trimmed cassidy's nails, but i am still afraid that if i let them out together a noise will startle cassidy and she will attack billie.
also, billie has actually jumped into the room with cassidy (sneaky cat) and there was no reaction

so my question is- what is the best place to reintroduce- my fear of reintroducing out in the main apartment is that it is a less controlled environment, and that they may attack and chase eachother, whereas if it is in the 2nd bedroom- i can easily toss billie out/shoo her towards the door if things don't go well

advice? right now cassidy is out in the apartment, and billie is in bedroom- cassidy is sitting infront of bedroom door very calmly....

thanks in advance!

Judging by the tone of your note you already feel like the best place is the 2nd bedroom because of the ease of removal if anything goes wrong. But it really sounds like everything should go well and like you have done a great job of taking care of things.

thank you so much for the reassurance!
after i read your post i decided to stop being so nervous, and just try and see how it went. so i gave cassidy a special treat, and let billie in- they didn't even look at eachother hardly- they just ate their treat and billie poked around a bit, and then I took billie out!
i am going to gradually increase their time together, and keep up the treats.
what a relief! i finally feel that things may be normal again if i just keep taking it really slow!
thanks for your help!!!