James Martin Davis, the attorney for 26-year-old Kelsey Peterson, said his client will plead guilty Wednesday to federal charges of having sex with a minor across state lines.
It's similar to the original charge of crossing the border to have sex with a minor but doesn't carry a minimum 10-year-sentence, Davis said.
A message left for the U.S. Attorney's office in Nebraska on Tuesday wasn't immediately returned.
Peterson and the boy left Lexington in October. They were found a week later in Mexicali, Mexico.
The boy, who is now 14, has told The Associated Press that he didn't consider Peterson his girlfriend but that they did have sex.
Davis has maintained that the law under which Peterson was being charged was inappropriate because it was intended to combat forced prostitution.
"She's always said like I did, she'd plead to what she did do, but she wasn't going to plead to what she didn't do," Davis said Tuesday.
Davis said he expects his client will spend six to seven years in prison.
He said he hopes state charges, which include kidnapping and first-degree sexual assault, will be dropped. An after-hours call to the Dawson County attorney's office on Tuesday wasn't answered.
The Associated Press previously named the boy as police were searching for him but stopped using his name after authorities charged Peterson with a sex crime.
He was an illegal immigrant in the United States when he left with Peterson. He is back in Nebraska temporarily after being granted humanitarian parole by the Department of Homeland Security.
