Margaret Partington decorated her Datchet shop, Elegant Hats for Hire, with bunting and a window display of red, white and blue hats made by milliner Wayne Martin.
Mrs Partington said: "I have always been a royalist, I just think they're wonderful!"
She said The Queen wrote to her in 2006, telling her she loved being driven past Elegant Hats because it reminded her of being at Royal Ascot.
The shop, which was the first hat hire shop in the UK, was opened in 1975 in Buccleuch Road before moving to High Street, Datchet in 1994, and now has 2,500 hats for hire.
Royal customers have included the Duchess of York and Princesses Beatrice and Eugenie, and the shop also provided some of Kate Middleton's family with hats for the Royal Wedding, for which Mrs Partington also decorated the shop.
She said: "It's just lovely to have something to celebrate."
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