Poor baby! I'd deffinetly find a vet that will explain to her what is wrong. My 2 sibes went through false pregnancies, because Sarge got locked up with them (he's neutered though) when they were in heat... we try to watch them but somehow they both slipped out through the back door and got outside together.. at 6:30 in the morning :\ Then about 2 months later, Sheiba was panting, whining, gathering stuffed toys, protecting the bed, nesting etc. Then not too long after, Nali did it. It was so strange.
Good luck though! Keep us updated!