Shrinking violet 

A person(typically female) who shys away from any sort of confrontation. Typically, this person will not stand up for themselves or anything else. Opposite of bold, brash, or confident.

Lucy was no shrinking violet, she told it like she saw it.

Shrinking violet by Crashmeek February 12, 2019

shrinking violet 

someone who is shy, hesitant, or afraid to have a voice in social situations.

"try not to be a shrinking violet at the gathering tonight,
everyone there will be casual and no one will bite!"

shrinking violet by Polo March 26, 2007