If she wants to be more polite in the future in similar situations, I think your script is useful and I appreciate it. But I think since his behavior made her afraid, getting away quickly without concern for etiquette was the better move and she doesn't need to feel bad about it. It indicated immediately, if her instincts were correct, that she wouldn't be an easy target. If he was just trying to make a connection and fumbling, he discovered quickly she won't give him one, so he could go sit next to someone else.

(It's useful to keep in mind that he already was slightly rude by sitting down without a cursory "is this seat free" that would be a very basic manners for this situation. He didn't, and it's not evil or anything that he didn't. But when she got up and left abruptly she was at the same level of rudeness. I don't think either party needs to feel bad about it, tbh. Social fumbles happen constantly.)