This is a new designer for Margot (at least that I’ve ID’d) and it’s great to add another brand to the designer index!
Her shirt and pant look comes courtesy of the Matteau Resort 2020 Collection.
The last time I ID’d Margot wearing this brand was for a candid, way back in 2015! Although it definitely is possible she has worn this brand since then but I have yet to ID. With her look, she wore a pair of Loeffler Randall Penny Bow-Detailed Plissé-Lamé Mules in Gold. These are available for £335.