Some how she got it into her mind that touch means lick my hand once. Any ideas how to break this nasty habit? haven't ran into this issue before.
Do you use a clicker? If so you might be able to shape her approaching your hand - so click her before she licks and then when she is confident with the approaching your hand game you could let her "fail" when she eventually licked you.
Licking your hand can be self rewarding. What about teaching her to target a post-it note as a separate trick and then once she is absolutely solid on that trick put the post-it note in your hand. Then once confident with that you can fade the post-it.
Before trying the above I'd be tempted to try a quick cheat in case it might solve the problem... try putting your half cupped hand down on a surface with a treat locked into it using your thumb. After a lot of licking most dogs will get their nose under your hand and try to bump it out of the way. That's your moment to click and release the treat. Once confident with that you can start to gradually change the presentation of your hand into a more normal touch cue position.
Hope one of these ideas helps... please do let us know how you get on and what works for you!