It's probably the food - some cats eat their fill and no more, and others just keep pigging out (like Sigfried). But just to be sure... If your boyfriend can't take Maggie to the vet, please check her spine. I'm not a vet but I know that some cats appear to be getting bigger, but despite the protruding belly, their spine sticks out. My favorite shelter cat died a month ago from FIP. I though he was finally gaining weight (he had been sick for a while), but it was just swelling. So just in case, take a look. I'm almost sure it's just fat, but there are a often cases of coronavirus and FIP in shelters. We've lost a few to FIP recently, and they all had that belly.