I would weigh the pups to get an idea of how much she's actually eating in grams. If you're using the 10-15% of weight rule she could eat about 80-120g of food. Could be that she just happens to be a slimmer snake. Every animal is different especially when it comes to growth rates, but as long as she feels firm and eats well and gains weight instead of losing it she's probably okay. That in mind there should be people with more experience that should be chiming in here soon.
Sent from my iPhone using Tapatalk