The drugs ADD kids take for their condition are not sedatives. The same drug that works for ADD also works for Narcolepsy (People who have trouble staying awake). The drugs help the synapses in the nerves to fire correctly and with better connections.
Every child I ever taught who had ADD and was on drugs did better. The ones that did really well, were the ones who had supportive parents.
Drug "holidays" are a good idea for children... But I'd predict that you'll be a happier family if she does adjust to Concerta