Kat No Damage From a Syndra Ult?

Ulted a Katarina right after her zhonya she shunpo away.

Not sure, but does that mitigate the damage from the Syndra ult. Balls chased her through the Shunpo and my cd went down. So where was my damage?

I know as squishy as it was it seemed odd that she instantly rengaged on a no-heal comp at full health. They might have aegis'd some, but I really down a 4-5 ball rank 3 ult could have been stopped with a single aegis.