I've killed two that taped at 240 each (on the hoof). But a friend's wife killed one that was scaled at over 400# in Missouri
I know, I didn't believe it either.
Your friend lied or didn't use a scale or she shot an elk.
Or she really shot a 400# whitetail. Could be. Weird stuff happens. She did have it scaled, and it wasn't an elk.
There is a tape measure for "weighing" whitetails. Better than the hairy-eye ball method. You can probably google it. I bought mine for $1 from Pennsylvania game and fish or whatever they call themselves.