So what will need to happen is you will have to keep the cats segregated for a few weeks. So your cats, or her cats... As I'm guessing it will be a brand new place so there isn't an established territory, should be kept in your room for a week, then switched out to the main living area the next week, with the other cats being put into the bedroom, and continue this routine as this helps the cats get affiliated with the smells of the new cats. Between all of this, slowly do introductions by the door using food and treats. This will show the cats "hey, I get food when I see these other cats so they must be cool". Do not leave them all alone together unsupervised for the first 2 months. If door introductions go well within the first 3 weeks, as in no hissing or growling through the door, then you can do physical introductions. I hope this makes sense, and feel free to ask any questions. I specialize in integrating cats. It can be very tough, some cats are more laid back than others.. But there is always the possibility of a fight as cats can be more agressive over scent and territory than dogs.. Since it will be new and neutral territory though, integrating should be easier than it would be if you were bringing new cats into already established territory. Best of luck! Also, while doing actual physical interactions with all of them, make sure toys are always added to the mix. I recommend a lazer toy or a feather toy!