The key words in that rule are "Not challenging an opponent for the ball"
Kerr jumping in the air to try and get a head on the ball was an act of challenging for the ball in my opinion. I thought it certainly influenced the defenders reaction.
I can remember a situation this year where Krishna in an off side position jumped to try and head the ball. Didn't make any contact but was deamed offside for making an attempt for the ball from an off side position.
My argument is that with VAR and the new recommendation for linesmen to delay their flag in offside. Means this rule now probably needs revisiting because this kind of scenario is going to creep into the game more with play-on offside calls by the linesman.
Like I said very grey area for me now.
Oh I totally agree with you and it needs looking at, just want to point out something to you about she jumped for it. The Brazilian defender would have had no way to know that Kerr jumped for it, as she was a yard or two behind and jumped after the defender went up. Reply of it with VAR is here https://streamable.com/a7dzb