The Pistachio Prescription by Paula Danziger (1978, Paperback)

Cassie Stephens is dealing with a lot: She’s got asthma. She’s running for freshperson class president. World War III is being waged daily in her home, beginning at the breakfast table and ending with slammed doors at night. Her older, shorter, more beautiful sister never ceases to remind Cassie that she is a giraffe. Cassie’s not really sure how it started, but eating pistachio nuts always makes her feel better. No matter how weird it sounds, those little red nuts are just the prescription for Cassie’s troubles.