I would feel her tummy and see if she has "lumps" in it and watch to see if it moves around or shifts sides it centers on. Do her tits seems to be sucked on? if none of them, she might have lost the babies.
well i neva had a cat that was pregnant but the best way to tell is to feel in her belly for like lil bumps and if they move she is probable pregnant! if she eats more and seems to be lazy more than active then she is pregnant lol