(KCEN) -- Travis County Sheriff's deputies are investigating an assault on Gabrielle Nestande at the Del Valle Jail.

An officer saw a fellow inmate allegedly attacked Nestande on Saturday. Nestande is nearing the end of her sentence for a fatal hit-and-run incident.

Deputies say Rachel Castillo, 27, grabbed Nestande by the throat and began to punch her, hitting her in the head. She cut her forehead and left her eye. Her cheek was red and swollen.

According to arrest papers the officer who saw the attack broke the two apart. Deputies say Nestande immediately went to get medical treatment and Castillo was locked up. She's now facing more charges.

"We're still conducting our investigation, trying to figure out what happened, why it happened. But in this particular case not only have criminal charges been filed, but the inmate will be taken before a disciplinary review committee to look at what other sanctions she'll face like reduction of good time, things of that nature," said Roger Wade of the Travis County Sheriff's Office.

Deputies say Castillo had only been in jail since late August when Austin police officers arrested her on a series of misdemeanor charges. Nestande has been in jail since March serving a six-month sentence for the hit-and-run crash that killed Courtney Griffin.

"Generally you're safer inside the jail than you are outside the jail. It happens from time to time but much less frequent than it would out in the general public," said Wade.

Wade says Castillo faces up to a year in jail for the assault.