Does Irisalis have a dash?

The dash is Whirling Blossom Rain, and it fires homing petal bolts as you dodge. Irisalis spins and dashes in whatever direction you choose, so it doubles as an evasion tool that saves stamina, and during the dash she looses several homing bolts in succession. Getting out of the way and dealing damage happen on the same press.

That is why her kit leans on it so heavily. The standard pattern is to put a clone on the field first, then spam the dash with Whirling Blossom Rain. Irisalis has only one set of skills, so the dash is not something you can swap out.

How the dash feeds her clones

Her active Iris Clones fire floral beams at the target when a trigger lands, and each Bloomcluster beam carries 15 Might. Casting Whirling Blossom Rain is one of those triggers, alongside landing the final hit of a basic attack combo. Every dash with clones out is extra beams on top of the petal bolts, which is the whole reason to summon a clone before you start dashing.

Not settled: What sets off Bloom Cluster, the effect that makes every active clone fire a beam, is not settled. It is given both as the dash itself and as finishing a basic attack combo or casting Whirling Blossom Rain, so how many beams a dash adds in practice may differ from the pattern described here.