Any transitions, be it onset of puberty
or change of school or any such major changes in children of this age may bring about such changes. She will need to be assessed by a psychiatrist so that the cause of the problem can be found out.
Usually, the best evidence for treating children of this age for problems like this is for talking therapy (CBT or family therapy) depending on the problem. As my colleague has suggested, if the problem is severe, then only should medication be considered and medication in this age will need to be VERY CAREFULLY MONITORED.
Please consult a psychiatrist
and if possible and available, seek out CBT/family therapy depending on the outcome of the assessmnt by a psychiatrist.