Typically children can have variable bowel habits. Not going for potty upto seven days is normal. Check if she has hard stools because of which she may have a fissure. This makes it painful for the child to pass stools and the child avoids going to the toilet and the vicious cycle continues. See if there is bleeding too which would suggest she has a fissure.
Solution: give her plenty of water to drink and feed her bananas. That should help. Otherwise you will have to start her on stool softeners.
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