If the vet said she's pregnant, then she's almost guaranteed to be pregnant. A false pregnancy will show all the signs of pregnancy(i.e. weight gain, halted heat cycles, pinkening nipples), but when palpated by someone experienced, there will not be any lumps, so it couldn't be that, Tasha.
The breeder we got Trin from had that happen once--she let the mother and stud stay together through her pregnancy. The mama delivered four healthy, normal babies and one born premature that was completely hairless and required a ton of special attention. He eventually grew up to be a healthy, beautiful kitty who suffered no ill effects from the experience.
Stranger things have happened. That's just one of many good reasons to keep your pregnant queen inside!