When does the breeding season start in the Southern Hemisphere? Gaining 400g wouldn't be terribly hard. If you feed her a single small rat once per week, she might gain it in about 6 months or so. If this is a young female (less than 2 years old), I'd give her a bit more time to put on the weight for breeding. The general "rule" is 2 years old and 1500g. Now, that is by no means the law of breeding ball pythons. I have a 3 1/2 year old female that is 1350g and she's been breeding like crazy for a few months.

So if she's younger I'd wait a season and get her weight up a bit more. 1200 is a small female. There are older females that are just petite that breed just fine but don't rush your girl into breeding.