If you see the dialogue makes it quite clear that she blames herself for what ended up happening that it was her "mistake."
So in one way to another she gives us to understand that she could have saved souls from the jaws and she did not succeed.
That's what she blames for her.
PS: The comment of the tree stopped having value in Tasting.
She saved Tyrande and Malfurion's Ass several times.
Sending Maiev a message or giving the tree some more strength was not a great achievement.