I'm not a parent but I think it's alright to buy her sugary snacks. Maybe put them in a cupboard that is just for her. I don't think stashing food in her bedroom is a good idea--the idea that these are "hidden foods".
I'm a child who grew up in a household that had cookies. My grandmother always had cookies when we went to visit. Food was a reward. When I became diabetic I realized that my parents didn't really foster healthy eating habits. We don't even have cookies in the house now (or any junk food) and I don't miss it.