Hello, I'm Dr. Deb.
I recently came online and see that your question about Zoey hasn't been answered. I'm so sorry that you've had to wait for a response, but if you still need assistance, I'd like to help if I can.
It doesn't take much to stimulate vomiting in a cat but certainly ingestion of an iris leaf might cause mild to moderate gastrointestinal signs such as vomiting and/or drooling...perhaps even diarrhea
In most cases, the vomiting or drooling will be self-limiting but she may have developed esophagitis which is why she's still nauseous.
You can give her over the counter Pepcid AC (Famotidine) at a dose of 1/4th of a 10mg tablet twice a day.
This drug should be used with caution in cats with kidney
or cardiac issues but one or two doses of 2.5 mg isn't likely to cause any harm.
If she continues to feel nauseous, then something else may be going on and the iris leaf isn't likely to still be responsible. In that event, a vet visit may be prudent.
I hope this helps and that she's feeling better soon; again, my apologies for the delayed reply. Deb