that is a difficult question to answer not knowing anything about this child. addressing a child's hygiene habits (or lack of) is difficult some parents but important nonetheless especially if you are the one doing the laundry. have a sit down talk about the importance of bathroom hygiene not just for cleanliness and odor but for medical reasons. stool left on the skin will tend to burn. if she already has irritated skin this could be the reason she doesn't want to wipe now. give her some hydrocortisone ointment and/or a good barrier cream used for diaper rashes to soothe these sore areas. she is old enough to help with the laundry so it may be wise to have her wash her own underwear pointing out that if she wiped better they would be easier to clean. buy her some new undies. some really nice ones but only give them to her when this behavioral problem has been finally solved. be persistent in your efforts but don't punish. often it is best to reward for good or expected behaviors than to overly-punish or embarrass a child for unacceptable behavior.
do you have any information about why a child (female age <positive_smiley> does not wipe her butt when she poops?