Looking at some other powers, I think it would be possible to put something together like this.
* There are powers that have effects of "Make a secondary attack", so we can use that to simulate the multiple attack rolls.
* There are some conditions, similar to diseases, that read "and the target is effected by NAME (save ends). While effected, target is EFFECT/ONGOING, and that increased to ADDITIONAL on the first failed save."
So, it is a single attack power with "damage and named status condition". The power then has an effect of "Make a secondary attack" with another "on hit" with damage, and another differently named effect. Repeat for the tertiary attack.
Now, the rolls are not "simultaneous", but they all take place in one power. And as the additional attacks are effects (not "on hit"), they will always be rolled.
As each effect is named, it can be referenced separately, saved separately, and worsen separately. You can also take her other powers and give them "if the target is also effected by NAMED EFFECT, then..." riders.
Is that along the lines of what you are considering?