תרופות בשבת

Our ten-year-old daughter was diagnosed with attention deficit disorder and we have started her on Ritalin. In general, she takes the SR Ritalin in the mornings before she goes to school. Thank G-d, our daughter appreciates the benefit of the drug and ac- tually wants to take it on Shabbat (which was not the case in the beginning).

Our question is, is it permissible for her to take Ritalin on Shabbat as well, on the assumption that she will be more cooperative at the table, etc.? In other words, can she be considered in the category of a holeh she-ein bo sakana?