Wow, I was not expecting this many replies on here, thank you so much everyone for taking the time to help me!!
Entranced, I too love your mind

and I don't think the vet has ruled out much, since he always says "come back in a week" and they never take her back. I don't know what those diseases/disorders/illnesses are. I'm not really a cat person, just *this* cat's person, so if I did take her, I'd have a LOT to learn. Unfortunately our home is not that big. Sadie just got her first flight feather and I was looking forward to it but if we take in Kitty, we'll have to put that on hold. I agree it's much safer when the target isn't chase-able. Even my docile, sweet dog got a little predator-like/curious when my neighbor's Quaker was flying around in her house, so I imagine cats are pretty similar in that respect.
Michael, I definitely understand where you're coming from. It's very scary to be risking Sadie's life even if it means saving another. It's really hard to find a home for a sick and old cat though when there's free kittens everywhere. And I sure hope Sadie doesn't give me too much hell when she turns one, she's been quite the angel lately. Hasn't drawn blood on my boyfriend for a couple of weeks now! Although she did try to rob him of his baked beans:

And while I'm on photobucket, here's Kitty:

And me & Kitty probably 4-5 years ago:

Thanks everyone for giving me so much to consider. Ideally I will find her a home, I've had one offer from a friend, but we need to discuss it further. It wouldn't be fair to Sadie for her to live with something that wants to eat her. Well, I have a dog too, but my dog is not interested in her at all, she doesn't even look at Sadie. Never once tried to get her. If Sadie flies on the floor, Bonnie gets up and walks in the other room to get away from her like she's a pest. But I don't want to test this fortune/luck with a cat! If worse comes to worst, she will come home and I will be prepared for it now that I have learned from other cat & bird owners. Pchela, it's really hard for me to believe dogs kill birds more often, but I suppose it could be true!