Prior to buying that frog, if he or she wasn't fed very often and improper husbandry - It will stop them from growing to their potential caused my malnutrition, known as stunted growth. All frogs grow at different rates so you can't really compare one to another. One could surpass another one in a couple of months so it's all just a waiting game.

Calcium deficiency can cause them to appear weak from early stages of MBD. Lack of calcium and vitamin d3 to metabolize will result in that... Supplementing with calcium w/ d3 is a must and a multivitamin once a week. Try to get him or her on a healthier diet - the earthworms you can try rubbing up against her mouth with reptile forceps (tongs) and see if he or she takes it from there. Stay away from feeding her mealworms or waxworms for awhile; good that you realized to stop feeding him or her waxworms though.

If you need a few different brands of supplements and vitamins to buy. Let us know.