A 12-year-old girl who was allegedly sexually abused by a couple was forced to "swallow her own vomit", according to court documents.

Jennifer Stevens, 35, and her husband, Michael Stevens, 36, allegedly told the child that she would "lose her guardian angels" if she reported the abuse that occurred from the age of just nine.

The documents alleged that the girl told police that Michael would whip her and other girls with a belt, and that their food was limited.

The pair are facing one count each of gross sexual assault for the abuse that allegedly occurred between 2010 and 2014 when the girl was younger than 12, according to a court order obtained by the Kennebec Journal.

It is not clear how the couple, from Waterville, in Maine, knew the alleged victim, who is now 16 years old.

The couple originally appeared in court last month but a judge ordered the affidavit sealed for 30 days because the case involved "very deviant conduct" with young children.

The document, written by Waterville police Detective Kyle McDonald, detailed allegations against the couple after a referral from the state Child Protective Services division.

The affidavit affirms that the couple sexually assaulted her for years until the abuse stopped when the child moved into a homeless shelter in Waterville.

It is alleged that Michael would beat her "with a belt" and that if she did not want to participate in the sexual abuse she was told she could "go clean the house".

The complaint said the child would get so sick after the abuse that she vomited and "was made to swallow her own vomit" by Michael.

Michael also allegedly "made her swear on her guardian angels that she wouldn't tell anyone" about the abuse and that she would "lose her guardian angels" if she revealed what had happened.

Lawyers representing Jennifer referenced her having a "heroin addiction" but neither defendant is facing drug charges at this point.

As part of the abuse the girl claims that she was forced to watch movies about exorcisms, according to the affidavit.

The couple remain in custody and are expected to return to court in April.