I'm not going to be much help either, but I know when Goofy first started hanging around my mom's house, he was a skinny thing and then all of a sudden he ballooned up and got the biggest tummy on him! Obviously he wasn't pregnant because he was a he and had been fixed, but he sure looked like he was! And his stomach was hard too. Turns out he had worms. It took awhile to get rid of them, but now he's a sleek, fit cat.

So, if nobody else comes up with a good way to tell, you might want to trap her and have a vet check her out and if it is just worms, you can always treat and release her. But if she is pregnant it sounds like she's due any day now, so you might want to trap her just to be sure.

Good luck!