Assaultin/Killing your opponent is an automatic loss.

You can counter a wild draw 4 by also playing one, in which case the next player has to draw 8 cards. So if the POV character is to move, Osaka having a wild draw 4 for would turn what’s a sure victory for the POV character into certain defeat.

(Of course, I can’t actually know what Osaka has on her hand. I just figured her having a wild draw 4 would be funny in this situation)

You win the moment you discard your last card. So the POV character plays +4, she counters with +4 and wins.

Her last card is also a wild draw 4.