It doesn’t matter if you agree or readers agree. A judge would not agree, and this would be a civil matter which would most likely simply go before a judge. A judge would not find enough evidence in common phrases and statements to say that it was plagiarism. Lifting a sentence here or there and writing pretty much everything else isn’t legally plagiarism. Writing a blog about people “stealing” and then accusing someone of doing said stealing in it when in the end it’s not legally provable does put you in a position to be counter-sued for defamation and/or libel. They smeared her name by accusing her of something that they really cannot prove in a court of law
If she agreed that it was plagiarism, then she’s foolish – though she was most likely doing it simply to get people to stop harassing her.