It is uncommon for Ritalin to be stopped at any specific age; children usually stay on the medication until such time they are able to regulate their own concentration and behaviour - which in some instances may only happen in adulthood. Remember that we do not outgrow ADHD.
With the increase in pressure of a higher grade, she may be finding it difficlt to keep on top of everything. From your post I do not know what therapy she has been through, but cognitive behavioural therapy may be worth a try; alternatively she may require beginning the medication again - not necessarily Ritalin.
I would suggest speaking with the doctor/psychologist who diagnosed her initially and the prescribing doctor (if it someone different) and get their input on how you should procede.
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