Maria Bazan was at her home in the Hidden Glen Mobile Home Park on the night of May 5 when her boyfriend, Angel Reyes, allegedly doused her with flammable liquid and set her on fire.
Officials said it appears Reyes came to the home, poured gas all over her and the home, started a fire, locked the doors and left.
Neighbors saw the smoke and ran to the woman's rescue.
"She tried to escape, but she couldn't, so the neighbor tried to break the window open with a bat and she got out from there, and she came into flames," witness Eric Chavez said on the night of the fire.
Bazan was taken to Harborview Medical Center with serious burns. She died at the hospital on Sunday, according to Ed Troyer with the Pierce County Sheriff's Office.
Reyes is being held in Pierce County Jail. His bail was set at $1 million.