Hi, welcome to Yorkie Talk.
What is the consistency of her poop? Is the poop mushy or hard? If the hair on her anus is trimmed off and the poop is firm it should fall with no problem. If the stool is soft or lose it could stick some to her skin. It is hard for me to answer without knowing how her stool is.
I do know that some pups can tend to get constipated when going through the weaning process. If she is constipated then she needs more fluids. Make sure she has a small bowl of water available. Also a little corn syrup in the water will help soften the stool.
If her stool is loose or soft then that could be caused from over eating or from coccidia. Have you had her stool checked by a vet? If her stool is soft or mushy then I recommend you get her stools checked right away.
Please keep us posted on how she is doing.