Here's what happens:
* Chapter 23 focuses on Katniss and Peeta finding shelter in a cave. They come across evidence of Foxface's survival skills and ingenuity.
* Foxface is mentioned as having already taken a poisonous berry from a nearby plant, but there's no indication she has consumed it.
* The chapter ends with Katniss and Peeta realizing they are being hunted by the Careers.
Foxface is later killed by Cato in a later chapter (Chapter 25) of the book. This is just after Cato is knocked unconscious by a spear from the gamemakers.