breasts that are shallow to the point of almost being invisible - like those of a slim prepubescent or peri-pubescent girl. Breast buds are characterized by their shallowness (closeness to the chest), not by their narrowness. Long, narrow breasts are not breast buds.
Though Donna was in her mid-30s, she had dieted so assiduously that she had the body of a 14 year old ballerina and the barely perceptible breast buds of a prepubescent girl. However, when excited, her nipples became hard like two halves of an unripened plum.