A Westbrook woman who is accused of allowing her boyfriend to sexually assault a 14-year-old relative with developmental disabilities backed out of a plea agreement on Tuesday and is now scheduled to stand trial next month.

Holly Morrison, 34, of 110 Brown St. appeared in Cumberland County Unified Criminal Court for what was scheduled to be a change of plea and sentencing hearing before Justice William Brodrick.

But Morrison’s attorney, Amanda Doherty, told the judge with Morrison at her side that Morrison had changed her mind at the last minute.

“My client informed me that she is not ready to move forward,” Doherty told Brodrick.

Morrison has pleaded not guilty to a six-count indictment brought against her in April for three counts of gross sexual assault, a felony punishable by as much as 30 years in prison, and three misdemeanor counts of endangering the welfare of a child.

The prosecutor, Assistant District Attorney Michael Madigan, told the judge that under the terms of the plea agreement, the maximum sentence she would have faced was a 15-year sentence, with 10 years in prison and the remaining five years suspended during a four-year probation term.

Madigan said Doherty could have argued for a lesser sentence and the ultimate decision would have been up to the judge.

Morrison walked out of the courtroom after the hearing, free on $500 bail, pending jury selection for her trial July 14.

Morrison is accused of watching her boyfriend, Donald Cass, use objects to assault the girl at least three times last fall, according to court records.

Westbrook police were first alerted by school officials on Nov. 14, after the girl told friends and a counselor that she had been assaulted by Cass multiple times. The girl also told officials that Morrison insisted she get in bed naked with the adult couple and shower with them, according to a report by Westbrook Detective Steve Crocker.

Cass, 59, of 57 Towle Ave. in Auburn, was arrested in the case last year and pleaded guilty to two counts of gross sexual assault.

Cass, a former reserve police officer in Auburn, was sentenced on Feb. 24 to serve four years of an eight-year prison sentence, with the balance suspended for a four-year probation term.

Morrison told police that she met Cass at a “swingers party” and they participated together in swingers’ events.

Cass, who is married, told police that he would visit Morrison’s home on weekends while telling his wife that he was going on hunting or fishing trips, according to court records.

As a condition of bail, Morrison was ordered to have no contact with Cass or the victim in the case.