Chulita has this tendency, but it's not out of control. I've taught her "enough" with some other things and it is a little skill that she's generalized. So, if I'm around and she licks too much, either a human or the couch or something, I tell her enough and she stops.........until the next time. LOL. (nothing like sitting down on a wet couch) I have a little trouble with her licking other people because they always say, "It's okay." LOL. Oh well...it's not the worst behavior in the world, especially with such a teensy tongue.
If this friend can distract her dog and have a treat ready...but make the dog wait without licking for just 3 to 5 seconds, then reinforce, eventually the dog should get the idea. Gradually increase duration that she must refrain from licking. It's kind of like bark training. She can even show the treat to distract, but not furnish it until those 3-5 seconds of non-licking are up. A split of a second before showing the treat, say, "enough" or whatever cue she's going to use. Later, when the dog is catching on to the game, the treat should not be shown to the dog but taken from random places. By this time, the cue, "enough," the stopping licking and the reward should be making a connection for the dog. Remember to gradually add duration and gradually remove the visibility of the treat. Still later, the treats can start being spread out, but still given sometimes to keep the skill fresh.