Omg, I used to get horrible attacks right when all the stress was over too.
Imitrex made me sick as a dog. Nausea and tightening of the chest. It was awful. The only protocol that has worked from me in a headache cycle (my attacks are cyclical--several months every few years) was Calan (verapramil) as a prophylactic and Fioricet for the actual attack. After several weeks on the Calan, I no longer would get attacks. Calan is a medication that slows down your heartrate. It's primarily used for high blood pressure, but neurologists use it for migraines.
KK, your daughter might be too young for Calan, but it's worth looking into, if the Imitrex becomes ineffective at some point.