Tell the backstory of your character and what her wounds are.
From there will come the FATAL FLAW.
What is the FATAL FLAW?
The fatal flaw is both a curse and a blessing in your story. The Fatal Flaw is a crucial element in your character that defines her to the core; something that is within her and only her, and will consume her.
On the other hand, the Fatal Flaw could be the key to unlock the deepest emotions of your character and forcing her to admit truths she has been denying for years.
You CANNOT create an interesting character without a Fatal Flaw. A story is about drama, drama is about the defaults lying in characters, and characters need to tell their story about their Fatal Flaws. If you create a character who is too plain, the fans are not going to understand and will fail to read your stories.
NO FATAL FLAW:
Check every single story and manga you have ever read, and even in streams of consciousness storylines, you will always find a Fatal Flaw, also called a Character Flaw or "Hamartia".
Examples of FATAL FLAWS
Hamlet (Shakespeare, play written circa 1599 ~ 1602).
Despite all what had happened, Hamlet doesn't take action.
The Lord of The Rings (J.R.R Tolkien, novel written between 1937 and 1949).
The ruin of Frodo Baggins is the One Ring.
Skip Beat! (Yoshiki Nakamura, manga currently being published).
Kyoko Mogami's fatal flaws are first her total trust and gullibility, and then her inability to love.
Lost (J.J Abrams, US TV series, 2004 - 2010)
Jack Shephard's fatal flaw is his desire to save everyone from themselves, whatever the consequences.