To me it looks like it's not a bra but not a proper top either. A little bit underwearish, but so what? She looks/looked fine.
The airline treated her like shit though, and have quite rightly said sorry to her.
She is a very sassy, outspoken young woman who refused to take any shit. Good for her. I would have cried at that age, if it had been me. More young women should be like her; not taking shitty behaviour lying down, and standing up for themselves.
Weirdly, a man on the plane, who was 12 or so rows back, had a pair of shorts on and a sleeveless vest. Nothing was said to him though. Hmmmmmm... 🤔
Misogyny at its finest! 