I think Mayson's labeling Superman as a vigilante had less to do with his powers and more with his anonymity. Can there be due process when the person making the citizen's arrest is anonymous? The scenario I see is Mayson outing herself to act "within the system" and then losing the powers.
Maybe better still, after her powers wore off having them restored for some time limit only after she has been in Superman's immediate vicinity. (Whether Clark knew it or not.) It'd give Clark something else to worry about. Without powers and her identity known she would be a target. Hang around Mayson and risk Lois on a rampage.
