I bought this dress for Vesper (Sonali) to wear and the hat fits her head perfectly and feels quite secure on her. Maybe Rebecca's head is bigger than Sonali's head???
The dress is a gorgeous color with gold emblems on it and is a very unique design. I did remove Vesper's underpants because the fabric on the dress is sheer and when they were on there was a panty-line across her abdomen. I don't know if that is the case with Rebecca's undies.