Sofia's face is wide and her hairstyle in favour for such a tiara. I have difficulties imagining it on Letizia's head because the tiara is so big and wide, her facial features are more in favour of small pieces.
Yes, Letizia's slight build and features would be weighted down by such a huge tiara. Letizia needs more delicate and refined jewelry. The shape of necklace and earrings would be OK though. I feels nice large pins would be more her style with longer flirty earring to match. JMO