So... does her ultimate proc the effect 3-7 times? (depending on the amount of spheres spawned) As her ultimate isn't exactly Periodic damage like Singed poison, its a 0.1 second cooldown per hit spell.

Does anyone know?

If so, Syndra could effectively decimate opponents with a 15/30%-35/70% burn out with just her ultimate - Thats not including the actual damage from the Dark spheres.

Reapplying Liandry's Torment merely refreshes the duration it has no influence on the passive's damage rate.