Unfortunately I don't think she will be up to breeding size by next season, that's not a bad thing really its better health wise to wait longer and to grow up slowly (i can't prove that but Its what I believe). I personally would feed her every 6-7 days. Your feeder size sounds perfect, a 40g rat is about the right size to feed. Some people go by 10% of the snakes weight but its roughly the same if you go by the thickness of the prey.

Good luck and lets hope she continues eating like a horse!