This is indeed a big problem for your daughter. She is already 13 years old and it is very important to help her to overcome this problem. Soiling like this is known by the medical term of 'encopresis' I presume that she has been seen by a paediatrician about her encopresis in the past. Usually in older children encopresis has a psychological cause. It would be best to take her to see a clinical psychologist ASAP.
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