I want her to like she does in the stories since that is the Elizabeth I'm used to.
She should have dark brown chestnut hair, with maybe a little wave to it, and down her back but not to her bottom. I would like big brown eyes as well. I think she can have an open mouth to her face. Even though she is shy. she still isn't insipid. She's more timid than Felicity but she enjoys her antics and likes a good time.
I think a smile showing a little teeth would be fine.
Since she is usually in that yellow colored dress in the books thats what kind of a dress I see her in as well.