At this age and stage of potty training it is very common for children to sneak off to a private place when they have to poop or to have a bowel movement in their pants (or, yes, even on the floor). So, in short, everything you are going through with your grandchild is normal.
To help her through this stage, you may need to have an extra dose of patience, since she is likely struggling with the issue herself. There are some common reasons why toddlers are unwilling or unable to use the potty for bowel movements including the following:
- Not Able to Get Comfortable. Your child may need to be more secure and comfortable on the potty for a bowel movement than when urinating. If you're using a potty cover for the regular toilet, be sure that it is the right size (so a toddler doesn't feel like she will slip through if she bears down). Also try using a step stool or similar prop under your toddler's feet to help her use the muscles she needs. If you have a portable potty, again, be sure that the seat is comfortable and that her feet are touching the floor.
- Not Sure How Others Do It. The fact is that children learn mostly by imitating others. It's not unusual for parents and caregivers who have taken a toddler into the bathroom to watch them pee never think to take that same child in while they are having a bowel movement. So, yes, a toddler may actually not understand that the potty is used for both if she's never seen anyone use it for pooping.
- Feels Embarrassed. A child who hides in a closet or behind the furniture to poop may be doing so because he thinks of the action as something ugly or "icky" and doesn't want to be seen doing it. This may be a learned response. Sometimes, without even thinking, parents and caregivers might say something like, "Oh, baby went yucky, icky poops!" Try not to connect the dirty diaper to something disgusting (even if you are just being playful and silly). Instead, don't make a big deal over the dirty diapers at all right now. If you find her dirty, take your child to the bathroom gently and take off the diaper there. Then tell her, "We need to put this where it belongs." Drop the poop into the toilet and flush it with a cheer, "Yeah. Goodbye, poop."
- Feels Scared. There are a number of things that toddlers find scary about pooping on the potty. From the loud noise of the toilet, to the isolation of the bathroom, to the scratchy toilet paper. The best approach is to make the bathroom a comfortable place. You might buy some special books, comics, or magazines that are just for the potty. She can read them whenever she wants to sit on the toilet seat to try and poop. Keep flushable wipes on hand so you don't need to struggle to clean her with toilet paper (or take her to the changing table or wherever you usually go to change her diaper and clean her up there). Even if she doesn't go poop, praise her effort to sit still for 10 minutes or longer trying to go.
You might also try reading some potty training books like Everybody Poops (compare prices)or watching videos such as: