[souffle]

It is possible but it sounds more likely that Pepper has grown much bigger due to the fact she has been bullying Salt and stressing her out and denying her food.
You have done the right thing in separating them and it would not be a good idea to put them back together. It is VERY rare for Chinese females to live together after they are pups and they can fight very badly. Keep her on pregnancy watch for another few weeks and also watch for testicles appearing. It sounds unlikely she is pregnant though if they are both still looking like females.