Yep, at 6 months old he/she is starting to go through puberty, and his/her behavior is very typical hormonal-behavior for a Green Cheek; Bowie used to do exactly the same thing, he would lean over and get his body almost horizontal, and come charging towards me, one of the other birds, etc. and then "chomp!"...
This is going to continue until your bird is at least around a year old, the first puberty is the worst hormonal period for any bird, but it's extremely important that you nip this in the butt right now, so that she knows that biting is not allowed, hormonal or not.
****Green Cheeks are "velcro birds", meaning they love attention and interaction, and they absolutely hate it when it's taken away or they are ignored. So in my experience, the "Shunning" Method works very, very well with Green Cheeks, as well as very quickly. It's easy, as long as you and everyone else that interacts with her follows the plan every single time she bites you/them. Whenever she bites you or anyone else, you immediately need to say the same phrase firmly to her, not yelling, but firmly, something like "No Bites!!!", and then you immediately put her right down on the floor, and then turn your back to her. And then you have to completely ignore her for 5 minutes. Don't make eye-contact, don't look her direction, keep your back to her or just walk out of the room, totally ignore her calls or screaming to you, say nothing and pretend she doesn't exist for a full 5 minutes. Then once the 5 minutes is up, go back and pretend like it never happened. However, if when you come back to her she just bites you again right away, then once again you immediately say "No Bites!", put her right down on the floor, and turn your back to her and ignore her again for 5 minutes. Then again start over...They usually catch on to the idea very quickly, as they hate being on the floor, lower than anything else in the room, and they hate being totally ignored. This will eliminate the biting pretty directly.
As far as the hormonal periods/episodes go, there are a few things you can do to try to ease them. Make sure that she's getting a full 10-12 hours of dark, quiet, restful sleep every single night. And putting her on a "Natural Light Schedule" will help tremendously.
****With Green Cheeks especially, you must make sure that she doesn't have anything in her cage or have access to anything outside of her cage that is a small, dark space that she can get inside of or under, as this will put her into a horrible hormonal RAGE immediately; Green Cheeks are very prone to this, so this means eliminating any tents, huts, hammocks, etc. inside of her cage, nothing made of fabric/fleece or anything that is fuzzy that she can sit on/get inside/get underneath, and nothing outside of her cage like getting into boxes, under furniture, etc.