I'd agree on a size (US) 4--I think that's a UK 6. She's very much built like a high fashion runway model and that's around where they hover, at least the ones on the thinner side. I do miss the 90s with 'curvy' (I know--ha-ha) models like Cindy and Susan Holmes.
This reminds me that recently Gwyneth Paltrow talked about what she eats on a daily basis on some podcast and she eats nothing.

IIRC, she said she has coffee in the morning, bone broth for lunch (tries to play it off as soup), and vegetables for dinner and on top of that an hour of exercise and time in the sauna. How is her body not failing? I know Victoria Beckham has revealed that she only eats steamed vegetables and grilled fish or chicken every. single. day. I hope that was hyperbole/joking. Former Victoria's Secret model Bridget Malcom said she didn't have a period for years due to her diet and workouts. BTW: I'm not saying that Kate is doing a Gwyneth or VB.
https://people.com/health...get-malcolm-losing-period