Introducing female kitty to another female kitty?

the following articles from SPCA will help you a great deal...

http://www.sfspca.org/resources/library/for-cat-ow...

http://www.sfspca.org/resources/library/for-cat-ow...

Sometimes it takes more than overnight for introductions. Normally you lengthen the visits as you see progression with the cat's tolerance of each other. It usually takes 2-4 weeks for things to calm down between them. There will almost always be some degree of hissing. Both the cats should be spayed. Feliway diffusers are really good for introductions as well. They release calming pheromones into the air and soothe anxiety. You can get one at most pet stores.

A bath won't hurt if your allergies are flaring up. I rescued two kittens once who had been doused with hoochie perfume and I had to bathe them. They were fine. After the bath, you might rub some corn starch into her fur to help absorb the scented oil from the shampoo. Brush it out thoroughly after it sets for a while.

It may be the smell, but also its a new cat in your 'older' cat's terf. She's protective of it, so you need to keep an eye on BOTH of them. I suggest IF you MUST give your cat a bath, to have the water already in the tub BEFORE you get the cat, otherwise, you will wind up with a lot of scratches and one totally and utterly PO'd cat! Give it time, but if they don't get along a few months from now, you may want to think about whats best for your cat. It takes a while for cats to warm up to new cats, took my 12 year old about 6-8 months to totally accept two kittens cause she was Queen for so long.

I have introduced young and old cats together many times. They will be fine. It's good you got your first cat another buddy, as they need other cats arounds. You can bathe her, but it's not that big of a deal. She will be fine. Good luck!