They tend to slug out (drop bad, unfertilized eggs) when they are on the thin side. Breeding is very taxing on their system and fat reserves, and many don't feed during breeding season, so your 1200gram girl now could be 1000-1100 when it comes time to actually ovulate and develop eggs. Just keep your temps up over the winter and feed the crap out of her, getting ready for next year. It will be here before you know it.