I can answer this! And the answer is no, immortal magic still affects Adhara.
Basically, Mordecai only prevent magic from being cast, while Adhara prevent it from existing all together. So, if a magic missile was cast just outside a Mordecai's range, it would be able to pass through his field and hit him- but if the same mage tried that on an Adhara, it would dissipate as soon as got near her.
I hope that helps!