My apologies, I should have explained more fully.
If you go to Google Images and search for "Wedding mood board" you will see that it is merely a board with pictures, maybe fabric swatches, which shows the 'mood' that you are trying to create for whatever occasion you are planning for. It provides a visual representation to show others to demonstrate what you are trying to achieve.
You might add things as you go along - for example, after you had decided on the flowers, you might add photos of the color and type of flowers that you were having and then if you went to order the cake, those flowers or the color of the flowers might be replicated on the cake.
Creating a mood board is a highly personal thing, so I'm pretty sure that Kate created her own wedding mood board. We also know she knows a little bit about art. This, plus the fact that she does not have a dedicated stylist/dresser supports the idea that others here have put forward that a lot of how Kate looks, the colors she wears, the clothes and accessories she chooses, comes from directly from her. Yes, she may have input from others, or get suggestions from various sources, but it does appear that a lot of how she looks - her style - comes from her.
Edited to add link re: Kate using mood boards:
Kate Middleton Had