Yes, the outfits for Ramandu's Daughter look very nice, and I'd hope we did see something of her as a young Queen and as Caspian's bride. The tiara you showed was nice, but I didn't like the three sprigs sticking up. I thought they made the tiara look too tall. I don't know what these pointy bits are called precisely - not arches. I'd think that Ramandu's Daughter would wear a tiara that from afar looked a bit like
this one, called the Halo Cartier Tiara, but I'd prefer to see something that retained the leaves, foliage and colour of the one you've already shown, but definitely not a tiara that looked too intimidatingly tall.
There are other types of tiaras such as
the tiaras on this website. Anything that looked as heavy as what the Queen wears would not be suitable in my opinion. These tiaras, on exhibition in London last year, which the Queen often wears on coinage and stamps, seem nowhere near as tall and complicated as those worn by her sister, grandmother and sundry other real life royalty. Crown Princess Mary of Denmark has one called the
Midnight Tiara which is supposed to gleam "lustres of lights and shades, like a starry, moonlit sky at midnight" and she has another one with oakleaves and rubies, both of which I thought looked a bit like Narnian jewellery but still too heavy.
Of course you don't do the real thing for a film.