The GOAT title goes to Kimberly Ann Gallagher.
At the end of Kim's senior year, her name was on the T&FNews top-10 list in the 4x400, 4x800, DMR, 800m, 1500, Mile and 5K. I guess a lot depends on what you call a H.S. athlete; in Kim's case, she was coached by a H.S. coach; she ran all of her high school meets and almost always tripling. In fact, when she ran the H.S. record in the mile, it was part of a triple at a sectional meet. When the record was broken a week later by Polly Plumber, Kim's response was I wish someone had told me to run faster. She only lost to one H.S. athlete in an individual event in 3 years, she set multiple H.S. records, Penn Relays victories, WJr 800m champ, and record holder. In 1982 Kim's 800m HSR would have won the NCAA meet and her 1500m time would have placed 3rd.