"she's very protective of and attached to us, and our son in particular. She hates to be separated from us, especially from him. She learns quickly, but does have a stubborn streak. She's very affectionate. Her energy level is really high, and she's very agile"
Look up silken windhounds. What you're describing sounds like a sighthound (especially the part about being stubborn!), and the size, body, and coat make me think of silkens. Is she pure white? If so you ought to contact someone from the International Silken Windhound Society. There haven't ever been any pure white silkens, and if that's what you have you could really freak some people out!
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Kadee Sedtal