The mother of a Brooklyn woman killed in a subway tragedy in Union Square remembered the 21-year-old aspiring actress as an “amazing, beautiful” person who died after “a bad day at work.”

Helen McDonald-Phalon, 21, was on the No. 4/5/6 platform around 3:30 a.m. Saturday when she somehow became wedged between a train and the platform, according to police.

The train was already moving out of the station when McDonald-Phalon made contact with the side, according to the MTA, which is investigating the incident.

As the train pulled out of the station, she fell onto the tracks, where she remained for almost 10 minutes until the operator of another incoming southbound 6 train saw her and stopped, authorities said.

“She was amazing. Beautiful. She was a light. Everyone who is getting in touch with me is telling me how their lives would not be the same if she weren’t in them,” her mom, Ann McDonald, told The Post on Monday.

“She was a loving, kind, amazing, beautiful, talented woman, and she slipped on the train and the train took off and that’s it.”

Her daughter had been a singer, dancer and actress since her childhood, the tearful mother said, and had moved to the Big Apple right out of high school to start a career in musical theater.

“She was working and just trying to make it. She had a bad day at work, some customer was rude to her, and she went out to blow off some steam and she slipped on the subway and fell,” McDonald said.

Phalon worked at the ThinkGeek at Broadway and 34th Street.

ThinkGeek, which caters to computer enthusiasts, described the young woman as “one of our lead geeks.”

“She was an amazing person to work with and simply a good-hearted individual,” the store posted to Facebook on Sunday.