See, I always thought she looked great in that picture. You can't see her ribs at all. She just looked 'fit'. Now sure, she didn't have much muscle mass yet coz she'd been kept in a small enclosure, but she didn't look thin to me. But that's just me I guess.
Your horses are lighter built too, they aren't a heavy breed. Your perspective looking at her would be different than a QH type. I'm a mutt in what I like. I like Arabs and lighter built horses to look at, but I also like sizeable ones to ride :~D Light horses make me look fat :~D