What Alice Wore to the Palace

Alice Temperley, one of my favourite designers (for the label Temperley London), was awarded a Member of the British Empire (MBE) for her services to fashion, which she collected from HRH the Queen on her visit to Buckingham Palace yesterday.
Often associated with wonderfully feminine, beaded dresses, it was a surprise to see Alice in a menswear-inspired suit as she went to the palace to receive her honour. I have to say that I love the fedora - a MUST have piece for this winter. And I applaud the practicality of a trouser suit since bending and curtseying is all part of the process. And it does look hot.
But suitable for the palace. Appropriate for a meeting with the Queen? I don't know. What are the rules? What do you guys think about this outfit and the occasion? Are there actually any rules anymore?