I bet she was bloody freezing on the plane
Or maybe not. I usually travel on other airlines, simply because they're more likely to be going where I want to go, and am always freezing, but just last week I went on a rare Thomas Cook flight and it was absolutely bloody boiling. I took my hoodie off and sat there in a t shirt, which is unheard of.
I wouldn't be offended at that outfit and logically I can't see how it differs significantly from a vest that would probably only cover up slightly more of her.