Hi
Our son has also suffered with SVT - mainly in his first year of life when he was prescribed flecanide. It took ages for anyone to even believe that there was anything wrong with him because the SVT made him very sick and the violence of the vomiting had corrected his heart-rate by the time a Doctor arrived and being a baby he couldn't tell anyone! After a year he was taken off the medication to see what would happen and has not needed to go back on it again since. He is now 11 years old. However, he does still have the occasional 'do' and we have found that putting a packed of frozen peas on the top of his head and sitting him down quietly does the trick. We have bought special packs which once activate by shaking freeze immediately, for him to use if he is out playing or away from a freezer!
I think it depends on how often the attacks happen as to if medication is necessary. We were told that we needed to consider the effect the SVT had on our son's life and the possible side-effects of medication and to decide on the best course of action for him. We were also told that stress may possibly bring on attacks but have not found that to be the case here.
Have you tried lowering the dose of medication or even taking her off it to see what happens - frequency of occurence etc. ? obviously with the Doctor's approval and support.