However, to Ms Westcott's "embarrassment", she was then informed that the mysterious man was Nicoletta's boyfriend, and the pair was just having a laugh.
"I could hear what her boyfriend was saying and he really didn't sound like her boyfriend," Ms Westcott added.
The situation blew up on Twitter when Nicoletta posted about what happened.
"Ricky was just acting like he wasn't my bf at the gym, saying to me 'you look nice in those leggings, can I take you out some time?'" she wrote.
"This girl (that I don't know) comes up to me and says 'hey you ready to leave?' I informed her he was my bf BUT GIRL I APPRECIATE YOU."
The post was retweeted more than 126,000 times and "liked" by almost 700,000 people. Many shared their stories about sexual harassment and praised Ms Westcott for her actions.
However, Ms Westcott said she was "extremely embarrassed" by the situation at the time.
"I was honestly happy that he was her boyfriend because I knew she was safe and wasn't getting harassed and something bad wouldn't happen to her," she wrote on Twitter.
She then explained why she intervened.
"There are a ton of really creepy guys who go to the gym and some of them don't really know personal boundaries," she wrote.
"For an example, the first time I started going to the gym older men would compliment my figure and say really weird things that would make me uncomfortable.
"I worked at a gym where a woman was raped in the locker room, and in the parking lot. And if other people were aware of their surroundings they may have been able to stop it from happening."
In reaction to the story, women on Twitter shared their stories about unwanted attention and how they have been helped by strangers.
"Was being stalked on a train before, and some random women helped me. Never been so appreciative in my life," wrote one Twitter user.
"One time at a bar a guy had cornered me and I must have looked really uncomfortable, then a guy neither of us knew tapped him on the shoulder and said something like 'hey, do I know you?' The guy turned away long enough for me to bolt. Extremely thankful," wrote another.
Despite the short-term embarrassment, Ms Westcott said she was glad she stepped in.
"All and all I thought it was appropriate because I didn't want another girl to be uncomfortable," she wrote on Twitter.
"I would rather be mortified with embarrassment than to have her in danger. Embarrassment goes away pretty quickly, having someone assault you doesn't."
Where to get help:
If it is an emergency and you or someone you know is at risk, call 111.
• Women's Refuge: 0800 733 843
• Victim Support: 0800 842 846
• Lifeline: (09) 522 2999
• Family Violence Info Line: 0800 456 450
