CW, so glad to hear that you liked Belle! I am going to chime in to support you in your decision not to sign a lease until you've seen her ridden by the owner or ridden her yourself. In my opinion, a good owner would want to see how you handled her, and would understand that you needed to ride her before signing the lease. After all, you want to ride, not to train a project horse! If she's not responding to you, maybe you could call or e-mail with some compliments about how much you liked her, loved her color, etc., so that the owner knew you were still serious about leasing the horse.
I agree that her grumpy face doesn't necessarily mean that she won't be good under saddle. It just means that she doesn't seem to be an outgoing horse - or maybe didn't know what a camera was! You will win her over in time, I'm sure, as long as she's not truly mean or ill-mannered!