Hatchlings and small juveniles can go quite awhile without pooping. This is because they are using almost everything you feed them to gain weight and grow.
Since your little female is already under weight she may not have anything to poop out.

Also from seeing your pics and reading your other thread; if I remember correctly you said she was 8-9 months old and 150 grams; I would try to get her switched over to rat pups and get her on a 5-7 day feeding schedule.