Can a Woman Be Too Modest?

In my recruitment work at Orot, I often need to photograph students in various educational settings at the college. I have found that a great deal of the students simply don't want to be photographed.
Orot's student body can generally be defined as very religious Zionist. Our students come to the school specifically because they're looking for a Torah-oriented atmosphere, as well as fellow students who share their values. I have no scientific evidence, but it seems to me that Orot students refuse to be photographed more than the average female population. And, while I'm happy to honor their wishes and never take pictures of unwilling students, I have recently begun to wonder: why are so many frum girls camera shy?
I fear that their shyness comes from a misplaced understanding of tzniut.
Among the numerous ramifications of the laws of modesty, halachah makes very specific requirements about female dress, including what parts of the body a woman must cover and what's considered appropriate modes of dress. It's no secret that Judaism considers the human body private, a vessel to be saved for the privacy of intimacy, and not to be shared with the public at large.
Yet, I get the sense that we somehow muddle the message. Instead of teaching our girls that they should view their bodies, molded by none other than God Himself, as beautiful sources of pride to be saved and savored, they somehow understand that they should cover themselves because they have something to be ashamed of. So, if someone wants to photograph them, these girls feel that simply appearing in a photo is somehow a breach of modesty, and they refuse to allow anyone to take a picture of them.
I wonder: How do you instill in a young woman a sense of pride and self-confidence on one hand; that they understand their own beauty and self-worth; but at the same time the notion that their beauty is not something to be put on display for the world, but rather a quality to be cherished and saved for the intimacy and holiness of married life?
I want my daughters to know how beautiful they are, but not need to share it with the world. At the same time, I hope they don't feel that because we teach them to cover themselves, that they're doing so because they have something to be ashamed of.