This is a 400-800 runner who is on low mileage and moving up. If Linden Hall could run like 52 second 400 she would be giddy and it’d be a notably impressive off-event result like this. But she probably can barely break 55 if at all. 4:16 for Mu is nice.
Per IAAF website, Hall’s PB is 59.31 from Dec/19
Doubt very much that she could run 55