The above poster is not correct. That's a good way to sex COLUBRIDS (corn snakes, milksnakes, kingsnakes, etc.) but not ball pythons. You can check for spurs. If it has really large spurs (bony-feeling bumps on either side of the vent), it's most likely a male. This isn't always a good way to sex the ball python, though. Probing would be best. It's possible that her growth may have been stunted, but without knowing her exact age or size, I can't say.