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Pain while passing motion can be due to fissures. Stool softeners and local application of xylocaine jelly before passing stools helps give rest and heal the fissures. It could also be due to an abscess. Infected piles is another possibility. At times such a pain is due to compression of spinal nerves. Infection with herpes simplex virus can also be another cause.
It is difficult to comment without examination. Please take your daughter to a doctor for a clinical examination. Hope this helps. Take care!