The Winter Queen represents the Death of Nature and nurtures it’s rebirth into the realm of the Living… Elune being her sister and counter part must represent the Life and rebirth of Nature, and as such she is wildly powerful (the winter queen power is determined on the amount of “life” within her plane then Elune must also) due to the sheer quantity of life within the Universe, however she may be limited in that power. As she literally is the goddess of Life and Rebirth, she is incapable of using her power to cause death and this is what the Night Warriors are. They are mortals not bound by the rules of Elune but granted her power to in-act vengeance… which is why Elune is sprouting the whole “Tyranda invokved her and must choose”, because it has to enitrely by Tyranda decision to kill as Elune is incapable of doing so…
It also make sense that that her tears (tear of elune) are a pillar of creation and was able to bring life back to the heart of Ardenwield because it’s literally her power of life and rebirth…
Elune an actual Goddes but is still limited by the rules of the First Ones it seems.