Short answer
No, a small sprig of cilantro is safe for a cat of any size. The risk from cilantro is very low, as it's not toxic to cats. For a tiny cat, just offer fresh water and watch for mild stomach upset. If she acts normal, there's no need to worry, but contact your regular vet if you see vomiting or diarrhea.
Cilantro — Food safety facts
Safe to share · Cats · full breakdown on the linked food page
Safe in small amounts. Not the same plant as toxic lookalikes such as hemlock.
The full verdict, portion guidance and serving notes are collected on the Cilantro food facts page.