Baby ball pythons of either sex can grow extremely fast, depending upon how they're set up & fed (more emphasis on feeding than setup!). I don't know if you can really cite an "average" growth rate for an animal that is an opportunistic feeder. We've raised both male & female ball pythons to around 3' in length in under a year, so it's definitely possible. You'll see her growth slow down a bit within the next 6 months to a year or so, and then she'll steadily get bigger over a longer period of time.

K