did foxface know that the berries were poisonous....???

She may be clever but there different kinds of cleverness. The way she is clever is the fact that she is slick and can move with ease without anyone noticing her. She is able to find the fundamentals of traps and codes. What I would describe her as, in your guys' terms is like somewhat, a hacker. Get me? She wasnt nature-clever but she was technologically savvy. Catching on?

wanna hear my thoery?
OK so my theory is that foxface did know that the berries were poisonous, she knew that the end was coming, were all the big fighters come out to play, and she didn't want to die by the Capital 's hand so she did suicide rather then be killed

here are some opinions link

She had no idea

she was smart and survived for pretty long so my guess is it was a suicide act

I do not think FoxFace knew the nightlock were poisonious
Even though she's very clever she was stalking Peeta and she saw him take berries and she thought they were safe and she was probably very hungry anyway so i don't think she knew the berries were poisenios