The teenager, who was visiting her mother who lives in nearby North Delta, had not brought any ID with her for her jog, but still tried to explain the situation to the border patrol.
She said she hadn't seen the signs while jogging along the beach and assumed it wouldn't be a big deal.
They detained her, keeping her in custody for two weeks.
A U.S. Customs and Border Protection representative told The Post that it was incumbent upon those traveling near the border to carry identification at all times.
"I said to myself, well I may have crossed the border, but they'll probably only give me a fine or they'll tell me to go back to Canada or they'll give me a warning", she told CBC.
United States Customs and Border Protection caused an global incident after detaining a French citizen jogging on the beach in British Columbia, Canada.
Documents issued by the U.S. government and shared with Radio-Canada confirmed that Roman was discharged on 6 June.
As she was jogging up the coast on the evening of May 21, she made a quick detour to avoid the incoming tide and then stopped to take a photo of the pretty scene.
Instead, the agents detained her and sent her to the DHS-operated Tacoma Northwest Detention Center, located more than 124 miles south of the U.S.
The US border agents stopped Roman and said they caught her crossing into the US on security video. "They asked me to remove all my personal belongings with my jewelry", Roman said. "I understood it was getting very serious and I started to cry a bit".
It wasn't enough; staff at the centre said the documents would have to be validated by immigration authorities in Canada before they could release Roman, according to Ferne.
She was held at the center for two weeks before the matter was resolved and she was allowed to return to Canada.
At about 9 p.m. on Victoria Day, Ferne received a call from her daughter bawling, telling her that she was detained in the U.S.
That was not to be the case, according to US immigration officials, who confirmed the subsequent events in an email to The Washington Post.
"It's like a trap. anybody can be caught at the border like this", Ferne told CBC. Neither agency would comment on Roman's case, citing privacy concerns.
A US Customs and Border Patrol representative said in a statement to the CBC: "It is the responsibility of an individual travelling in the vicinity of an worldwide border to maintain awareness of their surroundings and their location at all times to ensure they do not illegally cross the border".