I know when Pervy was expecting she got really big. Towards the end when she would lay still I could lay my hand on her tummy and feel the kittens move. I don't remember her getting a real hard tummy until the last couple weeks. I figured I would be able to tell how close the time was based on her teets. NOT! She was so stretched that I couldn't tell she had milk! Her teets are always real pink anyway so I was at a loss for awhile as to whether she was pregnant or not, until the very end.
I know I have not helped you at all but it sounds like your kitty might be. Can you trap her and take her in just to find out? You could always bring her back if she is just a pudgy!!