I don't know for sure who made Sarah's scarf, but I think it is a Prova scarf, just not from the mass produced Prova for Barney's collection.
PROVA scarves by Irini Arakas (ex Vogue editor) are simply amazing one-off, hard to find tribal looking scarves or foulards with fringing, made out of vintage dresses etc. Very few places stock them, though KirnaZabete has in the past.
If no one else knows can positively identify you could contact [email protected] and find out if Lane Crawford stocks them
Sarah is definitely wearing a Prova scarf. it is from the higher-priced Prova scarf collection that is sold at Lane Crawford, Ikram in Chicago, and Kirna Zabete. it is a vintage abstract camo silk with black and white fabric fringe.