You'll just have to go slow and steady. Keep her isolated in her own room for several days to a couple weeks before you have supervised visits (with her in a cat carrier at first). When she is in her own room, rub towels on the cats (or let them sleep on a towel for a while) and put the two resident cat towels in the room with her so she can get used to their smells and put her towel out with the resident cats to get used to her smell. I think the most important is to keep her in her own room for several days so she gets used to the idea of moving first, then introduce the other cats later on. You'll have to keep an eye on her and spend time with her. If you find she isn't eating or using the litter box within 24 hours, you'll have to coax her and work with her. You can get an appetite stimulant from the vet (Cyproheptadine) if you find her appetite is really diminished. Play it by ear. But isolate her for several days before any introductions. And, plan to spend a lot of time with her the first few days to get her comfortable. The other cats will be fine -- they have your boyfriend and are in their own home. Dote on her up front and make her feel safe in her own space and comfortable up front and it should work out when you start slow supervised introductions after a few days.
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Tammy

Stanley and Pookey

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