Cat woes again!

I don't know where to put this. Guess here's as good as any.

Several months ago, friend "A" decided to move out of town to go live with her SO. Friend "B" and I were pessimistic about the outcome of this, but wished her well, said our goodbyes, etc. Well, 2 nights ago, B calls me with the news A is coming back to town. We talk about how we both knew it would never work for A in that situation and we feel bad for her, but glad she'll be back in town again. Then B casually mentions that A's cat needs a place to stay. B makes it sound like this would just be for a night or two at most. B explains that she is allergic to cats, and A will be staying over at her place that night. So, I say, sure. What's one night or two, right?

Well, A comes over with the cat and its quickly becomes apparent that she thinks I am going to take her cat forever!

WTF!

Its an older cat, and A has has it for 5 years or so. Now, she's just going to get rid of it? I can't handle another animal. I'll have the puppy coming soon, and I've got Rikki. I live in a small place and my income is as small as my place. I cannot properly care for three animals, especially an older one that may have to end up going to the vet more often.

I explained all this to A and told her that I could foster the cat maybe for a while, but she needed to find a permanent home for it.

Well, I don't even think I can foster it after two days trying to mediate between my kitten, Rikki, and A's cat. A's animal is declawed and timid. I don't believe in declawing, so Rikki has all claws and he is young and rambunctious, plus this is HIS territory.

I know poor A has had a very bad time. She lost 20 pounds that she couldn't afford to lose. When I spoke to her she looked incredibly exhausted. I hate to add to her worries by telling her she is simply going to have to take the cat back. I don't think B is allergic cats, she just doesn't like them and doesn't want one in her house.

I'm mad at B for not being upfront with me in the beginning. She didn't tell me the truth about the cat's status and I think she just told A that I'd said I'd take her cat on permanently.

I don't want to strain my friendship with A and B, but they have certainly strained it with me. Its not like I owe either of them this big a favor either. I loaned A $200 right before she left town and then told her to forget about it, because I knew she was in a bad spot financially. I've also done many favors for B, as well.

Help! What should I do?