SOLVED. A middle grade book about an eating disorder and family tragedy. [s]

[Ms.soule]

Possibly Red Rover, Red Rover by George Ella Lyon.

From NoveList:

In her second novel, the gifted author of Borrowed Children (1988) follows a girl through the wrenching changes she undergoes during the year she attends sixth grade somewhere in Appalachia. The unexpected death of Sumi's grandfather is only the first loss; her elder brother, Drake, goes off to prep school where he can study piano, and her best friend also moves away, leaving Sumi bereft of her only confidants and somehow unable to write to either. Her first menstruation is traumatic: shy and repressed, Mother tells Sumi so appallingly little that it is months before she learns that menses are related to bearing children. By that time, she is close to anorexia as well as depression. Yet through the absences, isolation, and failed communications, Sumi strives to pass the unexpected barriers of this watershed 1960's year on the way to adulthood. When she understands (thanks to a doctor) that she's just maturing and learns to eat again; trades in her flute for the guitar she really wants to play; and uses a foolish assignment (incorporating spelling words in a letter) to write a real letter to Drake, she's on her way to concluding a memorable year of grief.

[Rebecca]

Looks like this was reprinted in 1997 under the name The Stranger I Left Behind.