Rachael even admitted to keeping the incident hidden from everyone - which included her mum.
"A few of my girlfriends were hooking up with boys," Rachael explained to co-host and Bachelor alumni Tiffany Scanlon.
"One of the boys I wasn't really interested in. He pulled me around the side of the party in a very dark alley and sexually abused me."
When the party was eventually shut down, she was left alone on the grass "crying her eyes out", trying to come to terms with what had just happened to her.
One of Rachael's biggest fears was that the police wouldn't believe her, which is why she decided not to report her attacker.
Prior to admitting her horrifying ordeal on the podcast, the reality star said she had only ever confided in a psychologist.
Later posting to her Instagram Story, Rachael explained further why she kept it to herself for so long.
"So that's my story," she said.
"I didn't think I would ever share this with anybody and I have opened it up to the whole world.
"Everybody deals with things in different ways. I like to keep things to myself."
After going public with her story, she said she went through a "really confronting and weird afternoon".
If you or someone you know is affected by sexual assault or family violence, call the 1800RESPECT hotline or visit www.1800respect.org.au/. You can also call the Domestic Violence Hotline on 1800 656 463.
If you or someone have something to report, contact Crime Stoppers, call 1800 333 00.