I've watched in past years her watching multiple matches per day. When I'm watching the women's single final and then watching the doubles' finals they'll pan to the royal box, and often she is at the doubles' finals as well. She'll go back stage to congratulate the winner of the previous match, then she'll return to the box to watch the doubles match in progress. She's also a doubles fan. For example, when Catherine, Meghan and Pippa attended the women's final together, Meghan left after Serena lost, but Catherine and Pippa stayed for the doubles finals.
Like I said there was a Brit, 2 Aussies, a Canadian, and a New Zealander playing today in the doubles. As a tennis fan, it would have been very difficult for her to leave without watching that. Less pressure with tomorrow, since if she's tired after the men's match, there is no realm country in the Mixed Doubles Final afterwards.