When they nip too hard, the other pup will let out a loud "Yelp!". This lets the puppy know that they nipped too hard. This lesson that the pup learns so young carries over to when they are older.
When your dog licks you compulsively, you will want to mimic the lessons that the dog learned at that young age. Each time your Boxer licks you, you must show that it is not acceptable.
Let out a rather loud "Ouch!". You will not want to yell, but do say it firmly and loudly to get the point across. Then pull your hand back. This will remind your dog of what they learned when they were young.
Now, you must continue on and ignore her for several minutes. This means no talking, no throwing toys to her...nothing. You are doing correct training by offering lots of attention when your dog does not lick. The aspect of: Good behavior = attention and Bad behavior = no attention works very well in training. Continue with the positive reinforcement training as well.
This will not work in 1 day. However, you always do this training when your dog licks and offering praise when your dog does not... soon your Boxer will learn that licking = unacceptable actions and that not licking you = a lot of attention and praise which raises self confidence. Wanting to please you, they will work hard to stop the behavior.