Here's the motion to dismiss, since it's not available at the link from the article: https://assets.documentcloud.org/documents/20519858/3-22-21-...
The meat of the defamation defense is around page 27-28. The tl;dr is: Powell's statements were opinion, not fact, and she provided the factual source that she was basing her opinion on - classic free speech, classic defamation defense.
I certainly get the funny part about politicians(well, lawyers in this case) being untrustworthy, but defamation is purposefully narrow to allow more speech in the arena, not less. It's not so funny in a different case where a quack brings a defamation suit against the blogger exposing their product as bullshit, or when a giant corp decides to silence people online critiquing their awful business practices.