A nice job of trying to deflect from the point but it's not going to work. There are many potentially defamatory statements made by people under their own names, too, and very few of them get sued either. Defamation lawsuits are not common because often the potential damages just don't justify the expense and because the lawsuit will potentially air the defamatory statements to even more people, causing more harm than good. But my point remains valid: if I were to defame someone and they wanted to sue, the fact that I made the defaming statement under a screen name rather than my own name is not a defense to the lawsuit. The real person behind that screen name is responsible for that, thus showing the "associative connection" that you claimed did not exist.
As a public person she would have an extra hurdle to win a defamation claim because in addition to the other elements of a defamation claim under state law the U.S. Supreme Court has held that public persons have to also show the defamer acted with actual malice or reckless disregard for the truth. But if she did have a good claim, the fact that the defamer made the statement using a screen name would not shield him/her from liability for the defamation. Also, note that defamation made on a post in a forum like this would not be slander. It would be libel since it is written defamation rather than spoken defamation.
But the reality is that none of this really matters for the issue you raised about getting banned. The site is free to ban you, the person, from ever using this site if it wants, regardless of what screen names you want to use. You seem to have acknowledged that the site has that right, so the distinction you are trying to make really doesn't matter, does it?