After an emotional turn on the stand, describing being molested by a celebrity she had admired, Judy Huth batted back questions from Bill Cosby’s lawyers in court on Tuesday as they attempted to discredit her impassioned testimony about being sexually assaulted as a teenager.

Ms. Huth, often crying, recounted for the jury in Santa Monica how she traveled with Mr. Cosby to the Playboy Mansion in 1975, where she said she came out of the bathroom to find the entertainer sitting on bed in an isolated, adjoining room.

“He patted the seat next to him,” she said. “I sat down. He tried to lean me back, he tried to kiss me, he tried to put his hands underneath my belly button where my high-waisted pants were.”

To deflect him, Ms. Huth said, she told Mr. Cosby she was on her period. But then, she said, “he pulled his sweats down, grabbed my hand, put it over his hand, closed it” and forced her to perform a sex act on him.

Mr. Cosby has denied the sexual assault and on Tuesday one of his lawyers, Jennifer Bonjean, sought during cross-examination to undermine the credibility of Ms. Huth’s account, asking why she had changed the date when she said it had happened and accusing her of giving conflicting versions. Reading from earlier statements in which Ms. Huth said she couldn’t recall how she had felt in the days and months after her encounter with Mr. Cosby, Ms. Bonjean said they were in contrast to her statements at the trial, when she described being depressed and feeling isolated.

“It’s hard to keep lies straight,” Ms. Bonjean said.

“I don’t lie,” Ms. Huth replied.

Ms. Huth reported her accusation to the police in 2014, but prosecutors declined to file criminal charges because the statute of limitations had passed. But her lawyers then filed a civil claim because in California, the period in which one is allowed to file a lawsuit is extended for people who say they were abused as minors but repressed the experience and did not realize its traumatic impact until they had grown up.

Mr. Cosby’s team has challenged whether Ms. Huth had actually suppressed a memory of an encounter or whether she simply came forward with an accusation to join others who were providing accounts of misconduct by Mr. Cosby at that time.

Under repeated questioning from Ms. Bonjean, Ms. Huth denied that she had coordinated her 2014 account with a friend, Donna Samuelson, who had accompanied her to the Playboy Mansion on the visit with Mr. Cosby decades earlier.

She also denied that she and her friend had coordinated an effort in 2004 to reach out to a tabloid reporter to talk about the accusation of sexual assault. The Cosby defense has suggested the effort was evidence that Ms. Huth had a solid memory of her experience at the Playboy Mansion a full decade before she went to the police.

Ms. Samuelson had taken photographs of Mr. Cosby and Ms. Huth together at the Playboy Mansion, and Ms. Bonjean suggested the photographs were key to having the tabloid pay for an article.

“You told her you were poised to get as much as $20,000, and you told her you would share the proceeds” if she provided the photographs, Ms. Bonjean said.

But Ms. Huth, whose account Ms. Samuelson has supported during earlier testimony in the trial, said that was not the case.

Mr. Cosby’s lawyers have suggested that the encounter at the mansion actually happened years later than when Ms. Huth says it occurred, and that Ms. Huth was at the time an older, and willing, visitor to the mansion who by her own account did not flee after the encounter but stayed for hours.

During her testimony, Ms. Huth spoke of how she felt after what she described as a sexual assault. She was, she said, “mad — I felt duped, fooled. I was let down. I was hurt.”

But though she was “freaking out” and “wanted to leave,” she said Ms. Samuelson, who was the one who had driven them there, persuaded her to stay.

Ms. Huth’s lawsuit had largely been on hold for years while prosecutors in Pennsylvania pursued Mr. Cosby, 84, criminally on charges that he had sexually assaulted Andrea Constand, a former Temple University employee.

But Mr. Cosby’s 2018 conviction in that case was overturned last year by the Pennsylvania Supreme Court on due process grounds, and Mr. Cosby walked free.

Ms. Huth, 64, told the court Monday that she and Ms. Samuelson met Mr. Cosby on the set of a film he was making in a California park. Mr. Cosby, she said, invited them to his tennis club, then gave them alcohol at a house where he was staying, before asking them to follow him in their car to the Playboy Mansion.

The jury was shown a photograph taken by Ms. Samuelson of Mr. Cosby and Ms. Huth walking together outside at the mansion. Mr. Cosby later left for another engagement and the two friends stayed behind, she said, swimming in the outdoor pool. They ordered tequila sunrise cocktails and, when Mr. Cosby returned, watched a movie together until they left at around midnight.

Ms. Huth told Ms. Samuelson that Mr. Cosby had assaulted her, but she asked her friend, she said, to tell nobody because she felt embarrassed and blamed herself for being there.

In the years afterward, she said she buried the traumatic experience.

“It’s like trash,” she said. “You dig a hole and throw trash in it.”

In an effort to explain why she did not file suit until 2014, Ms. Huth said that it was a time when she saw many other women coming forward publicly to accuse Mr. Cosby of sexual misconduct and noted that her own son was turning 15. The emotional damage caused by the assault finally came to the fore, she said.

“I went into an emotional tailspin thinking about if something like that happened to him,” she said.

Mr. Cosby’s lawyers have noted in court proceedings that Ms. Huth’s recollection of when her encounter took place has changed. While she initially said it had happened in 1974, when she was 15, she more recently concluded it was in 1975, when she was 16.

Ms. Huth said she recently realized she had made a mistake, in part because she saw a photograph of Mr. Cosby from 1975 wearing a beard and looking like he had, she said, when they went to the Playboy Mansion together.