Female Albino Burm Small for her Size

[BurmesePythons!]

Hi all! I'm new to this forum. I own a female 2016 albino burmese python. She is about 5 and a half months old and only around 3'3. I've only had her for about 3 weeks but her previous owner said she fed her appropriately sized rodents weekly, but burmese pythons are supposed to reach 7-9 feet in their first year (especially females). At the rate she is growing, I'm not sure how that is possible. Right now, I am starting to feed her small rats every 5 days and she is in shed right now so thats a good sign, bu if anyone has an explanation for her size as well as if I should worry and what I should do to get her bigger, please comment.

Thanks!