What she did not know is that the leader of the Archinviel Adventure Group wasn't holding back in their fight he only fights in this way because he couldn't use most of his combat technique when his enemy was this person in front of him.
He could transform into a tornado right now but this only leaves him vulnerable to attacks from his opponent right now as both of them knew each other too well.
So he could only fight in close combat but this also cause his opponent to be unable to use some of his combat technique this even their situation.
As long as one of them shows weakness then the tide of the battle would definitely tip off.
They were so focus in their fight that like Shiro they forgotten everything around them even the deep water that was actually getting deeper as time goes by.
They did not realised this just because neither one wanted to show any weakness.