I read on here that salt isn't harmful to birds and that they need it. Peppy has started to look up at the cupboard where it is stored until we get her some out. Can I assume that she will only take what she needs? It is so funny watching her "ask" for it.
Klasing's book on Comparative Avian Nutrition says birds have a specific appetite for salt, meaning that they'll seek it out when they need it. This doesn't necessarily mean that they'll stop when they have all they need. One of those salt wheels made for rodents might be helpful, since a tiel has to work pretty hard to get the salt off of it and will be less inclined to overindulge. The brown kind is better than the white kind since it contains other minerals in addition to the salt. Don't give one to a large parrot that could easily snap off a large piece and eat it.
Another thing to consider is that the inside of the cupboard might look like an awfully nice nesting place to her and that's part of her interest in it. My cockatiels would certainly like to get into the cupboards.