Apparently she refused to greet the Trumps and the Queen "gestured" to her- I only read the briefest of articles.
I saw an extended video, the Trumps were the last people through the door to be greeted by HM, Charles, and Camilla. The Queen was asking if there were any other dignitaries coming, and Anne was gesturing that it was just her there. Looks like something different in the short clips which is what people ran with, but it's really not a story it seems.
She was also in the conversation with Trudeau and few others where they appeared to be talking about a certain someone's behavior at the press meetings earlier in the day.