Pennyandrocky is right green cheeks are clingy birds but they can be taught a degree of independence. The key is making other things exciting, with Ollie foraging worked well , trick training and playing games. We would hide treats in the toys on his playtree, at first we made them easy to find and put them everywhere, then we started putting less and less in and making them harder to get into. It got to the point that Ollie always spend ages looking for food even when we only put the odd treat in every few days. We also played another game (also foraging) called the bottle cap game, you should find the video if you do a search. Basically we lay out a load of bottle tops and hide treats under certain ones, Ollie goes round flipping them all over but if we leave them there I can guarantee he will keep going back on his own to check if he has missed any. Different sized caps slot in one another making it harder.
As for the landing on your head that will take time to teach her to land elsewhere, to start off with you need to teach a reliable step up and distract her from going on your head in the first place. Once you have a reliable step up you'll be able to let her land on your head and feel confident you can get her straight off again. After that you can start teaching her your preferred landing place.
Honestly I would say just deal with the poop, I know people do have potty trained birds but I feel it is unfair and possibly even harmful, they are not like cats and dogs who can go hours without going to the loo, birds go every 10-30 minutes on average. Even in humans holding on to waste can have a bad effect, constipation, water infections etc. With a bird there will always be accidents any way.
**EDIT** - link for game mentioned above
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