I have seen this issue come up a couple times. I'm actually dealing with it, myself. I have a female Granite, that I purchased from a VERY reputable breeder. When I got her, she weighed in at a whopping 12 grams.
I like to follow a slightly modified Munson plan, when feeding. I have seen my snakies grow steadily on that plan. Well, all of them except this one. She at first lost weight, then only maintained weight for several months. She actually didn't grow past 12grams for the first 4 months I owned her.
I decided to take her to the vet for a fecal. That came back negative for parasites. Great news, except that she still wasn't gaining weight. I contacted the breeder and she thought that I was dealing with either an over production of stomach flora or a very high metabolism.
She had me put the snake on a much more vigorous feeding schedule. I was feeding single pups that weighed 3-4grams, every five days. She was pooping them out within 24-36 hours after eating. So I bumped my snake up to feeding every 3 days, slitted every pink and used nutribac. I have done this for the last several months and seen her triple in weight. You could class it as a type of power feeding, but at this point, I think it was necessary.
The first thing I suggest is getting a fecal test done, to rule out parasites. If that comes back clear, then figure out how long after she poops after she eats. If it's a very short time, you are either dealing with a snake with a faster metabolism or the pinks you are feeding are too small. You can safely feed 24 hours after she poops, but don't do this, unless you have a real problem with weight.
Good luck!
Wayne