Thanks Everyone.
She seems to be doing really well, and doesn't seem distressed or anything about not having any babies. She is really quickly turning back into her old self: eating well ( although she is very unimpressed with having so little food, and no extras!) has so much more energy and personality, and is back to her usual 'spinning and singing' self when I pick up her lead indicating that we are going out!
Her abdomen has already started to reduce in size, and is no longer solid. The vet asked if I wanted some medication to counter her 'pregnancy' hormones, but I decided to just let her body sort itself out.
She is now on Hills R/D Prescription diet, as she has a considerable amount of weight to lose, and this diet is designed to make her lose weight without cutting out any vital nutritional needs.
Hopefully she will be back to normal in no time!