Nakasia James had been sought for questioning in the stabbing death of 21-year-old Dorian Powell in San Bernardino on January 11 2016.
Local media reported that police had been searching for the 18-year-old after learning of a posting that was reportedly posted on her Facebook page.
It read in part: “Last night, my ex was drunk ... was fighting me... hit me in the face... and I get the knife and stabbed him. Didn't think I would hurt him. Sorry, lord, hopefully you forgive me, and sorry, Dorian Powell. RIP.”
Ms James was taken into custody by Hemet police after officers responded to a tip, Lt Rich Lawhead, of the San Bernardino Police Department, told ABC News.
At about 2.35am, police received a call regarding a person “who had reportedly been stabbed by his girlfriend,” according to a news release issued that day.
Officers responded to the 2000 block of North Central Avenue, where they found Mr Powell suffering from injuries consistent with a stabbing. He was pronounced dead at the scene.
Later the next day, an apparent confession was published on a Facebook page purportedly belonging to a person named “Nakasia Macc James.”
The author of the post wrote that she had been fighting with her “ex,” who hit her in the the face.
“We was really fightn and I gt (sic) the knife and stabbed him,” the statement said, adding that she “ddnt think I would hurt him BT I did he died.”
Police have declined to comment on the social media post.