The 20-year-old filed a lawsuit against Bieber last week, claiming that she became pregnant after having sex with the popstar following an October 2010 concert.
Bieber's representatives immediately denied the paternity claim, with the 'Mistletoe' singer eventually insisting during an interview on Today that he has never met Yeater.
Yeater has now spoken out on the scandal for the first time and revealed the details of her alleged sexual encounter with Bieber.
She told The Insider: "He immediately took a liking to me. We just got to talking - it was me and him with other people elsewhere. He eventually asked me… 'Would you mind if we could go somewhere and be alone?'
"When we got to what turned out to be a bathroom, his whole demeanor changed. It went from cute and gushy to, just, more aggressive."
Doubts arose about Yeater's claims after it was reported that she previously accused a former boyfriend of being baby Tristyn's father.
However, Yeater insisted that her "allegations" against Bieber will be proven true when the case goes to court.
"I have provided evidence to my attorneys and it'll show in court [and] prove that my allegations are true," she said.
Bieber will take a DNA test to prove that Tristyn is not his child.
"We'll vigorously pursue all available legal remedies to protect Justin and to hold those involved with bringing this suit accountable for their actions," Bieber's publicist Matt Hiltzik said.
Yeater is also due in a Las Vegas court on December 12 to face charges that she slapped a former boyfriend during an argument.