Tuohy is the hs girls xc GOAT due to her three national titles, numerous course records and overarching arc of her career.
However, after Thorvaldson's 16:30 win over Brown's 16:56 at LCU's HS XC Invitational last month -- and now these historically fast track times -- if I had to choose who was the best on her best day, I would choose Thorvaldson.
Would also pick Thorvaldson over Hutchin's recent sub-16 as well as Amber Trotter's 2000 FootLocker w/180 speed rating.
However -- sorry to disappoint the younger audience on this forum -- but for the greatest single-xc-race in history by a US hs girl, still have to bow down in reverence to Melody Fairchild's 1990 Kinney National Champs win at Morley Field in San Diego. (Remember, no NXN back then -- Kinney was the national championship race.) Running 16:39/5k with those two Upas St hills -- on an 80 deg day and winning by 59 secs over 2nd place -- is still incomprehensible.