I have a sweet Bombay runt named Jane. She's 4 years old, and a total sweetheart. She's also a pretty anxious kitty. She was put into the shelter soon after she was born (Jane is a runt and slightly off breed, so not 'valuable' enough to keep ), and I get the sense that she was bullied by bigger, more aggressive cats in the shelter.
We've had her for two years now, and she's well acclimated to our family of 3 adults. We fostered a bunny for a few months, and she never displayed anything more than vague curiosity toward it. For a couple of weeks, she shared quarters with my mom's cat, a hand raised (and grouchy) Maine Coon named Bella. It seemed like Jane wanted to be friends, but Bella didn't. Such is life.
My roommate is considering getting a kitten. Jane has done well with other pets, but I've never acclimated a cat to a baby cat before. Are there any specific things I should or shouldn't do?
My biggest concern is that the kitten will be larger than her, or quickly outgrow her, and bully her. She's kind of a pushover. Is there anything I can do to facilitate a friendly relationship between the two? I don't want my Jane to get steamrollered like she did in the shelter!
I think extensive research through the internet and pet stores may be the most useful in these situations just to be safe. I can tell you though, when I was getting a new kitten the way I went about it was getting them familiar with each others scents first.
By this I mean, we had my older cat Lucky in one bedroom than would let the kitten run around the house and sniff at the door and such, than we switched and had the kitten in the bedroom and Lucky on the outside. When they seemed to be handling that okay we got an old Dog play pen and put the kitten inside that with one of us with her and had Lucky able to roam around on the outside. This allowed them to get near each other and see each other without having actual contact in case they didn't take too kindly to one another.
This method seemed to work out alright, and my cats had gotten along ever since. Of course this method might not work for everyone and you should go about it in whatever way you are most comfortable and to make sure both your cats safety comes first. Hope this helped with at least some other ideas of what you could do, or how to go about it.
Just take it slow. I've done it a few times. I usually kept the cats separated for a while at first, and then occasionally had them swap rooms so they could smell each-other. Try to do that for a little while, maybe a few days, and then introduce them. They might hiss a little bit, but just let them go with it (unless they actually start fighting, in which case separate them). They will probably avoid each-other and occasionally hiss for the first few weeks, but as time goes on they'll get used to each-other.
How they get along really depends on their individual personalities. If your room-mates cat does start to bully your cat, then you can correct the problem by separating them or otherwise negatively reinforcing the bad behaviour. I have two cats now, and one was 3 when I got the younger one, and they have never been best friends but they live in general harmony and occasionally chase each-other and play.
We never had experience with cats living together, we just have one serious cat which is 7 years old already. When we got Dodge, he's one bully and super playful jrt chasing Mr. Dart almost whole day and we know he will be just fine. Cats are good escape artists whenever there are trouble, just give them space. And of course, your need supervision to keep them from fighting and developing the habit. Most cats doesn't like water so spraying them whenever someone gets too aggressive can immediately interrupt.
I just had another thought - have you looked into a product called Feliway? It's a synthetic pheromone spray designed to calm cats. The vet I take my cats to uses it in their waiting room, and I have a friend who is having some problems introducing a new cat and is about to start trying it as well. You can probably buy it at a vet or a pet store, but it's definitely on Amazon as well: http://www.amazon.com/Feliway-Plug-In-Di...ds=feliway
Adding a Kitten with a Doormat Cat 
), and I get the sense that she was bullied by bigger, more aggressive cats in the shelter.
