Could be worms, could be a lot of things - I would definately take her to the Vet for a check -up. Once she gets a clean bill of health tyr giving her some ask the Vet for a few suggestions.
If she was declared healthy you might try and give her some Kitten Glop:
4 oz. plain yogart
3 oz. water
3 oz. condensed milk (no fat free)
3 large or 4 small raw egg yolks (never give raw egg whites to a cat)
Shake, then strain through small strainer to collect any eye white that may have slipped through first time.
I store in a jar with a tight lid.
Also, make sure she is getting premium quality kitten food. The cheaper stuff has too much filler and she might not be getting the nutriens she needs.
Hope this helps.