I can assure you that if I were responding to a purely scientific discussion by Ms. Smith, one which contained no polemics or personal shots against anyone, I would not use the expression “arrogant young twit,” and would not speak about her at all, but would simply address her scientific claims.
However, given that the piece of writing we are discussing did contain direct and indirect personal insults to another scientist, one cannot avoid having thoughts about her as well as about her scientific claims. And the thought “arrogant young twit” naturally springs to mind. There are other words that come to mind, based on other utterances. For example, if she indeed said what she is alleged to have said about another female scientist (see the website discussion linked by Ron), the words “potty-mouthed” and “vulgar” would naturally present themselves.
In short, ad hominem remarks (whether flattering or negative) have no place at all in a scientific discussion, but they are perfectly appropriate when the subject of discussion is not nature, but the behavior and character of another human being.
Is it “respectful” to call someone “arrogant” when that person is behaving arrogantly? Perhaps not, but if is truthful, why does that matter? Is it “respectful” to call someone “selfish” for double-parking and thus preventing another person from obtaining a parking space? Perhaps not, but if it is truthful, why does it matter? People who are behaving badly ought to be told they are behaving badly; it’s the only way they can learn to improve. My guess is that Ms. Smith, growing up, was not frequently told by parents, teachers, and friends when she was behaving badly, and thus never learned how to speak respectfully to people with whom she disagreed. But whatever may be the cause, it is not necessary to be “respectful” when one tells someone else to stop insulting people. One need not be vicious or brutal, but one can be quite blunt; and indeed, often bluntness is the only thing that works, when the person who needs the correction is proud and insensitive.