I'm so glad you took her in!
Keeping her separate for a couple of weeks is a GREAT idea. It will really help your intro go much better.
In the meantime, you can help them get used to each other and associate good things with each other.
Take a couple of rags or washcloths (preferable washed without fabric softener or something). Rub Sophia all over with two and rub your little ragdoll over with two. Take one that smells like Sophia and put it under your ragdoll's food dish. Also, twice a day at very regular times put treats down for your ragdoll on the other towel that smells like Sophia. If you can make one of those after a play session, that's even better.
Then do the same for Sophia. Put a rag scented like your ragdoll under Sophia's food dish. And at regular times if possible, put treats down for Sophia on the other rag scented like your ragdoll.
This scent-swapping will really help the two before they actually meet. I really would give it a couple of weeks. And then I'd take Sophia out of her room, and someone go into "Sophia's" room with the ragdoll. Let her investigate and smell everything. Maybe have a play session in there with her (when she's done sniffing everything).
I wouldn't let Sophia loose - maybe hang in the bedroom with her while ragdoll investigates her room. If Sophia wants to investigate the room, that's fine.
But after 15 mintues or an hour or however long ragdoll wants, then let ragdoll back out and put Sophia back in.
Also, after that, you can open the door a crack and let them smell each other. If there's no hissing, maybe you're ready for some supervised time together the next day: let radgoll into Sophia's room for 10 -15 minutes and see how it goes.
Cats are territorial, and in our experience, females do not handle intros to newbies as well as males do. So make sure you continue to shower your ragdoll with lots of love and attention - extra play time. Do lots of things to reassure her that she's still your number one baby.
But help her think that having Sophia around is going to be a total party. When they have their first supervised visit, if they're not hissing or bugging out on each other, maybe give each of them a new toy.
You can also get catnip toys - give one to Sophia and give one to your ragdoll. After they've slobbered and drooled all over them, pick them up, and a week later, give your ragdoll the one Sophia drooled all over, and give Sophia the one that your ragdoll drooled all over (cats become insensitive to catnip if it's left out).
The main thing is to not punish either of them for "bad" behavior towards each other. Cats are very territory-oriented, and your ragdoll being unhappy about having an intruder in hers - and one that it looks like is going to be staying - is natural. So the most important thing is to give them time, help them associate each other with good things, and through heaps of love and attention, help them both understand that sharing the space doesn't mean giving anything up.
for saving a kitty in need!