If Imperial Decree is active and I target twice with Bellows Breath an Irelia with GA, is she dead or only the GA?

Yes, your Irelia will be dead.

When you cast Bellows Breath with Repeat while Imperial Decree is active, you create two separate instances of damage. Each instance of damage triggers Imperial Decree, creating two separate "Kill" triggers on the chain.

Here is the sequence of events:

1. Bellows Breath (first instance) resolves, dealing 1 damage to Irelia.
2. Imperial Decree trigger #1 is added to the chain.
3. Bellows Breath (Repeat instance) resolves, dealing 1 damage to Irelia.
4. Imperial Decree trigger #2 is added to the chain.
5. The chain resolves in LIFO (Last-In, First-Out) order:
   • Imperial Decree trigger #2 resolves first. It attempts to kill Irelia.
   • Zhonya's Hourglass activates as a replacement effect, destroying itself to save Irelia from this first kill attempt.
   • Imperial Decree trigger #1 resolves next. It attempts to kill Irelia again. Since Zhonya's Hourglass has already been consumed/destroyed, there is no protection remaining, and Irelia is killed.

Summary: Zhonya's Hourglass is a one-time replacement effect. Because Imperial Decree creates multiple triggers from the multiple instances of damage, the first trigger consumes the Zhonya's, and the second trigger successfully kills the unit.