Kitty update - she's still with us, and as of yesterday, she's officially ours, as far as I'm concerned.
Yesterday was when I finally got up the courage to call the SPCA
I spoke to an employee there, gave her a description, she looked up reports of missing cats, and there was nothing close to a description of her. I asked the woman how soon people tend to report their cats lost, and she said within a day or two. Given the amount of time we've had her in the house, and she's been hanging around outside, she would have gone missing almost two weeks ago. I also asked the woman if I should take her to their offices to get checked for a microchip, and she said that if she's never been spayed, it's very, very unlikely that she'd have a microchip. As far as I can see/feel, there are no signs at all that she's been spayed, so I really don't think I'm going to bother. They have my name and number in case anyone calls to report her missing, but the woman seemed to think that at this point, it would be unlikely that they'd get any calls, and I agree. We also went to a pet store in our area yesterday to pick up some things for her, and the woman that manages the places reiterated this - she said that in the past year that she's worked there, there have only been two people coming in asking to post flyers for missing cats. It seems that cats are expendable to many people.
For the first two days she was in with us, she clung to us like crazy. We couldn't leave her alone, she's follow us everywhere. The odd time that she did stray off to explore the house, she'd quickly return to where we were. She went upstairs on her own a few times, and would be up there for a minute or two, then she'd start crying. We'd call her and she'd come running back to us. I think she got up there, realized she was alone and got scared. Yesterday and today she seems much more secure, coming to us for snuggles for a few minutes, and then moving away to lay a few feet from us, as opposed to right on us. Oh, and she likes to wake us up in the morning by jumping on our faces. lol
Here's a new pic: