She said she realized she was assaulted when she later read text messages among friends and saw a photo of herself and a video made that night.
Mays and Richmond are charged with digitally penetrating the accuser, first in a car and then in the basement of a house, while out partying Aug. 12. Mays also is charged with illegal use of a minor in nudity-oriented material. The two maintain their innocence.
The case has riveted the small city of Steubenville amid allegations that more students should have been charged and led to questions about the influence of the local football team, a source of pride in a community that suffered massive job losses with the collapse of the steel industry.
Earlier Saturday, defense attorneys went after the character and credibility of the alleged victim, calling witnesses to the stand to accommodate their schedule, although the prosecution had not yet rested.
Two former friends of the girl testified for the defense that the accuser had a history of drinking heavily and was known to lie about things.
On the stand, West Virginia high school student Kelsey Weaver said the accuser told her what happened two days after the alleged attack then, sometime afterward, told Weaver she couldn't remember what happened.
"So two different versions?" asked Mays' attorney Adam Nemann.
"Yes," Weaver replied.
Earlier, Weaver testified that the accuser was flirting at the party with Richmond.
Both Weaver and schoolmate Gianna Anile testified they were angry at the accuser because she was drinking heavily at the party and because of her behavior, which they said included rolling around on the floor. They said they tried unsuccessfully to get her to stop drinking.
Anile said she also tried to get her friend to stay at the party rather than leave with others, including the two defendants.
"When I told her not to leave, I was trying to, like, pull her back into the party. She was trying to shrug me off," Anile testified. "She kind of hit me."
Anile, whose lawyer was present during her testimony, appeared, like all of the trial's teen witnesses, reluctant to be there.
The day after the party, when Anile and another friend picked up the accuser from the house where she'd stayed, the accuser said she had no memory of the night before, Anile testified under questioning by defense attorney Walter Madison.
"'We didn't have sex, I swear,'" Anile said, describing the accuser's comment.
Anile said she'd seen the girl drink heavily in the past and that she no longer speaks to her.
The case has featured disturbing testimony from teens, both in person and in graphic text messages, and has shined an unwelcome light on what students in the community once considered private conversations. Some teenage witnesses winced at times as they were forced to read adult language from texts.
Anile repeatedly said she couldn't remember statements she made to police last September about the night of the party. Midway through her testimony, special judge Thomas Lipps agreed to let her listen to a 40-minute recording of her statement to refresh her memory.
On Friday, three teenage boys granted immunity for their testimony said the accuser was drunk and didn't seem to know what was happening to her that night.
Mark Cole, Evan Westlake and Anthony Craig spoke Friday of the West Virginia girl's behavior the night of a party and described her being digitally penetrated in a car and later on a basement floor.
Cole testified that he took a video of Mays and the girl in the car, then deleted it later that morning. He testified he saw Mays unsuccessfully try to have the girl perform oral sex on him later in the basement of Cole's house. Cole also testified that the girl was intoxicated and slurring her words.
Westlake testified he saw Richmond's encounter with the girl in the basement, as did Craig. Westlake also confirmed that he filmed a 12-minute video, later passed around widely online, in which another student joked about the attack.
Craig testified that he saw Richmond's hand in the "crotch region" of the girl, a less descriptive version than he gave last fall in another hearing.
If convicted, Mays and Richmond could be held in a juvenile jail until they turn 21.
The Associated Press normally doesn't identify minors charged in juvenile court, but Mays and Richmond have been widely identified in news coverage, and their names have been used in open court.