This is a PERFECT thing to use a clicker for.
Put the dog on a leash. Have SOMEONE ELSE hold the end of the leash, from behind the dog. (use a buckle collar).
have tasty treats in your pocket, and something with which to make your desired behavior. You can use a clicker, or you can use a verbal marker. I use the word YES!.
Let the dog come up to you and begin licking. Let her get in a couple of licks, and then have the person behind her pull her back just far enough that she has to stop licking. The instant she stops licking, mark and treat.
Then allow slack in the lead. If she goes back to licking, have the person behind her put enough pressure on the lead to stop her again. Mark and treat.
Goal being she will sit there on a loose leash and not lick. End the session when you get even a few SECONDs of her sitting there on a loose leash not licking. End the session with a jackpot of treats.
Once she will sit there for a few seconds without licking, you can start giving this a name. I like to think of cute names for behaviors that I'm going to be using around other people. You could say "zip it", or "stow it" or whatever you like. Just make sure she ONLY hears these words when she is NOT licking.
I bet if you are diligent and practice this for a couple of nights, you will have her up to a minute of so of not licking. Once you get to this point, start proofing a little. Move closer to her. If she does not lick, mark and treat. If she does, move out of her reach. ONce she is not licking any more, mark and treat.
I would bet money that in a short time too, you could shape her into "air licking", now THAT would be a cute trick. Think of a different word for that. Like "Raspberry". In seperate sessions, mark her for any showing of the tongue. You will be surprised at how fast she will learn to do these things if you just stay quiet, and mark the behaviors you want.