If the story is true it shows a stunning lack of empathy on the part of the "plus sized" passenger for an individual who paid for a seat and should expect at least a basic level of comfort during the flight. It's not possible to render a completely fair judgement without having been there to witness any interactions between the teen and her neighbors.

Taking the story at face value and the teen at her word, I'd conclude that the fat neighbor was already ashamed of being plus-sized but was so thin-skinned as to project the source of her shame onto an innocent passenger for seeking basic comfort instead of properly attributing her feelings to what may be a long, ongoing battle against her own obesity for which she was already intensely self-conscious.