"I'm so happy for Andrea," she tells PEOPLE exclusively. "I'm totally doing back flips. It has been such a totally horrific journey."
On Wednesday, incoming Montgomery County District Attorney Kevin Steele announced he'd filed aggravated indecent assault charges against Cosby for allegedly drugging and sexually assaulting Constand, now 42, at his Elkins Park, Pennsylvania, mansion in January 2004.
Coral Von Zumwalt
His attorneys released a statement late Wednesday to various media outlets vowing to fight the charge.
"Make no mistake, we intend to mount a vigorous defense against this unjustified charge and we expect that Mr. Cosby will be exonerated by a court of law," said the statement released by Monique Pressley, one of Cosby's attorneys.
Pressley also appeared on the Today show Thursday morning to defend her client, telling Savannah Guthrie, "My client is not guilty. And there will be no consideration on our part of any sort of arrangement."
Pressley responded to comments that the comedian looked frail when he showed up for his arraignment on ABC's Good Morning America.
"I don’t really understand it," she told the show. "He's a tall man of sufficient girth. He's 78 years old, and blind, so he does use a cane so that he can know what’s coming in front of him, and he does require assistance because of that, and that is who the DA's office has chosen to charge in this case."
More than 50 women, including Ferrier, have now accused the entertainer of drugging and/or sexually assaulting them. Cosby has vehemently denied all of the allegations.
Ferrier says she's only recently gotten to know Constand, though she came forward with a similar account of her own in 2005 to support Constand.
"She's been a pillar of strength for me personally," she says. "I'm so over-the-moon proud of her."
"When you go against the Cosby it's incredibly frightening," she adds. "He's very powerful and he can destroy you."
Matt Rourke / AP
She says she went to visit him in his dressing room in Denver in the mid-1980s and he gave her a cappuccino.
"I woke up in my car in the parking lot with my clothes all a mess," the model told PEOPLE in 2006. "I was definitely drugged. All I had to drink was coffee and the room was spinning. I wondered, I still wonder, 'What did he do with me? Why was my bra unhooked? What happened?' "
In excerpts of his deposition in Constand's case made public last summer, Cosby said he did not remember doing that to Ferrier.
Ferrier says she kept quiet about what happened to her until she read about Constand's allegations against Cosby in the National Enquirer in February 2005 and reached out to the tabloid.
"The only reason I came forward is because I'd never seen another story about a person who'd encountered Cosby and been drugged and assaulted," she says.
The Enquirer agreed to pay her $7,000 (which she says she never received) and asked her to take a lie detector test, which she passed, according to Ferrier.
Instead, according to court documents unsealed last summer, the Enquirer agreed to kill her story in exchange for an exclusive interview with Cosby about Constand's allegations, which ran in March 2005 after authorities announced they would not charge Cosby in that case.
"Sometimes you try to help people and it backfires on you and then they try to take advantage of you," Cosby told the tabloid. "I am not going to give in to people who try to exploit me because of my celebrity status."
Cosby also said in his deposition the story was read to him before it ran.
In a statement to PEOPLE, a spokesman for American Media Inc, which owns the National Enquirer, says the tabloid was "unflinching in our aggressive coverage of allegations against Mr. Cosby."
Mark Blinch / Reuters / Landov
Ferrier says she is as ready to testify today as she was when she first came forward nearly 11 years ago.
"This is like independence day – the moment we've all been hoping for," she says.
Several of the other Jane Does have filed defamation lawsuits against Cosby, and Cosby has countersued them. Due to the litigation, the alleged victims cannot comment about Cosby's arrest, says Joseph Cammarata, an attorney for seven of the women.
"This is a significant step which seriously undermines Mr. Cosby's public pronouncements of having consensual sexual encounters with Ms. Constand," he tells PEOPLE. "It has sweeping ramifications for all the pending cases against him."
Attorney Gloria Allred, who represents 29 of the more than 50 alleged victims who have come forward – though only one has a civil suit against Cosby – called the arrest "the best Christmas present they could ever receive."
"Many of my clients" are prepared to testify as witnesses in the Constand case if the prosecutor asks them to do so, she said at a news conference Wednesday.
In the meantime, Ferrier, who is represented by Allred but does not have a civil suit against him, says she will continue to campaign to get the statute of limitations for sexual assaults involving adults either extended or eliminated in Colorado, her home state.
It's an important issue, she says.
"If Andrea let this go, her statute of limitations date expires in January," she says. "She could not have done anything. She has to do what she has to do because now she knows there's [more than 50] of us and we're all depending on her and we'll be there for her."