Brand, now 51, is accused of raping the woman after meeting her at one of his Hammersmith Apollo gigs in 2009.
She has told Southwark Crown Court on Thursday she willingly engaged in a threesome with Brand backstage, then went to his Hampstead townhouse for sex a few days later.
But she says during the second encounter he turned a consensual sexual encounter into rape by forcing her into anal sex and ignoring her pleas for him to stop.
One of the woman's friends said she was a "bright, bubbly and confident girl" but added: "This experience definitely changed her."
She told jurors: "It's like she lost respect for herself after that day, she blames herself for what happened."
She said she accompanied her friend to a meeting with a Sunday Times journalist when she was considering speaking out about Brand but told the court she was trying to go sober and battling mental health difficulties at the time.
She said: "She is a vulnerable person.
"Her mental health was not great, she was in early recovery."
One of the alleged victim's work colleagues in recent years fought back tears as she told the court she had also been told about the "traumatic" attack.
"She is someone that has experienced great trauma, the subject matter is not pleasant, so her demeanour was reflective of that," she said.
The friend said she understood that Brand had treated her "quite harshly," adding: "He left her to clean up. I think she was crying at that point."
Another woman who had worked with the complainant said she was told Brand said "I will be gentle" but then went on to have anal sex with the young woman without her consent, the court heard.
The alleged victim's AA sponsor gave evidence that Brand had been "business-like," "very straight to the point and not romantic".
When she was considering speaking out to a Sunday Times journalist, the alleged victim wrote in a Facebook Messenger exchange: "I'm not sure my story has much in it," the court heard.
"I feel I was an idiot. I was young and stupid," and she added that she was "probably as much to blame".
Earlier, friends and family of the woman gave evidence that she did not go to police at the time of the incident because she did not think she would be believed.
The court heard her mother remembered hearing her daughter describe "screaming out in pain" while telling Brand to stop, while her father told her: "That is rape".
A friend also told the jury: "She didn't think she would be believed, and she didn't think it would be worth it to go.
"She kind of put it behind her."
Brand denies three counts of rape, three counts of sexual assault and one allegation of indecent assault, after being accused by six different women.
Jurors have heard he picked out the alleged rape victim in the foyer after the Apollo show, so that she and another woman could have a threesome with the comedian backstage.
In the second encounter, she claims Brand forced her to shower and brush her teeth before sex, and she says he forced her into anal sex despite her making it clear she did not want to.
Brand denies all the charges he faces, and says all sexual encounters were consensual but have since been "reimagined" by his accusers.
The judge sent jurors away until Monday, when the prosecution is expected to close its case.
Brand's defence case is due to start on Tuesday morning.
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
