was it a series where she appeared?
Yes, a  television series "Grey's Anatomy".
Lexie Grey
 medical drama television series "Grey's Anatomy"
when does lexie come in grey's anatomy The character is introduced in season three what features does this character have? Her character has been called "reliable, trustworthy, timid, and apprehensive" .The character has also been described as an "innocent young intern" she knows how to make good relationships
wiki:9163232
Lexie Grey [SEP] Introduction
Alexandra Caroline Grey, M.D. is a fictional character from ABC's medical drama television series "Grey's Anatomy", portrayed by actress Chyler Leigh. Created by series producer Shonda Rhimes, the character is introduced in season three as the titular protagonist's younger paternal half-sister. She transfers to Seattle Grace Hospital as a new surgical intern after her mother's sudden death, and is eventually named a surgical resident in season six. Leigh was originally contracted to appear for a multi-episode story arc but ultimately received star billing from seasons four to eight. She has also reprised her role as Lexie on the spin-off show "Private Practice".