Submission is pretty much the running theme here, and "enemies" are often not what they seem to be at first. You may also find you don't actually have that much of a choice anyway.
Currently she doesn't need to be interacted with outside of beating her once to get a dark spell book. I assume at somepoint she is going to become mandatory to have completed (as she has scenes talking with who i assume is demonking,) so evidentally those scenes have to be completed prior to being able to defeat the demon king.