I agree. If Diana were to make those kinds of remarks, it wouldn't have been around the Queen. The questioning about Sophie's class/salary/wages doesn't ring true to me. Diana had her faults, but no-one has ever accused her of snobbery.
i find it hard to believe the story about diana being so rude to sophie in front of the queen. diana won't dare because it put herself in such a bad light and the queen would be more incline to support sophie and believe the worse of diana.