According to her account, their initial jokes were based off of a conversation that she was directly involved in. Based on that fact, in her position I would not have considered their conversation private.

Furthermore they continued their discussion while the presenter was talking. That right there is going to annoy people around them, even if they had the most innocent conversation in the world. Which they weren't. In fact her description left me with the impression that she thought they were specifically joking about her.

Basic scenario. Off color jokes starting off of your conversation, that you feel are directed at you, by random strangers in a public space. I can understand her getting upset by that. She may have been mistaken in her impressions, but her unfortunate emotional reaction is understandable to me.