Paladin, it is a complete physical transformation.  A Lunar has to stalk their human prey for hours, kill them and then devour their heart’s blood.  The killing is ritualistic and is part of a spiritual ceremony that confers on them the shape of that person.  Further charms allow Lunars to age the person, alter small physical differences and even to assume their celestial patterns or what have you.  It is not a disguise.  She is using all the physical attributes of that person.  Obviously she is not using the person’s personality or mannerisms, but she isn’t trying to convince you of that.  The voice she speaks with is manufactured using a man’s vocal cords and shape.