Princess Sarvath as a foreign guest is held to a different dress code in the royal enclosure. They are permitted to wear the national dress or service dress of their own country. It seems under that rule, she isn't held to the hat restriction that other ladies are. I know someone like Haya would most certainly have worn a hat, but Sarvath seems a bit more traditional.
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As for the earlier children's question about George, and Zara attending as a teen: Children are permitted in the royal enclosure but on 2 conditions:
1. they must be 10 years of age or older
2. are permitted on Friday and Saturday only
I wonder if we will start seeing Louise. She often attends horse events with her parents and she would probably enjoy Ascot. They are held to a similar dress code, but girls are allowed to wear fascinators and head pieces until they are 18, not proper hats.