Yep, welcome to a combination of puberty/hormones and typical Green Cheek behavior that needs to be changed through Positive-Reinforcement training only (NO punishements or negative-reinforcement at all)...As Chris said, there is ALWAYS a reason why your bird does what she does, you just don't understand what those reasons are...And she doesn't understand what she's is and is not to do. So you need to start Positively-Reinforcing all of her good behaviors, and totally ignoring the bad behaviors.
It's not at all uncommon for birds to be territorial about their "Territory", which for them is their cage, and that probably isn't going to change much. I have an almost 4 year-old Quaker who I've had since she was 12 weeks-old and who is a little lovebug that is extremely bonded with me. However, I just cannot put my hand inside of her cage when she's also inside of it, I have to respect that her cage is her territory, and if I do that then she respects that I need her to come out of her cage when I open the door and take a step-back. So I positively-reinforced her coming right out of her cage every time I open up the door and take a step backwards. So she will come right out as soon as the door is opened and I step backwards, and when she does that I tell her to come, she flies right to me or she'll just step-up for me, I give her a Training-Treat, and then I change her food/water and clean her cage while she's either on my shoulder or playing on her stand. So if that doesn't change and she stays territorial about her cage don't be surprised, but that doesn't mean that she has to bite you every time you want her to come out of her cage or every time you need to give her food/water or clean her cage. You just need to positively-reinforce what you want her to do when you open that cage door, and totally ignore her and her any unwanted behaviors when they occur.
If you haven't already, you need to choose a "Training Treat" for her that you will keep in your pockets or within reach at all times when you're at home with her, and that you'll be giving her from now on whenever she does what you ask her to do, or she just does what she's supposed to do. Whatever you choose as her "Training-Treat" needs to be something that she absolutely LOVES to eat, that is small and that she can eat very quickly on the spot, and that YOU NEVER GIVE HER ANY OTHER TIME EXCEPT AS A POSITIVE-REINFORCEMENT FOR HER GOOD BEHAVIOR, and that's it. It must be a special treat that isn't a part of her regular diet or even a "regular" treat or goody she gets at other times. Depending on which bird we're talking about, I use raw, unsalted Sunflower Seed Kernels, raw, unsalted Almond slivers/pieces, human baby whole-wheat "Puffs" that you can buy at any grocery store or Walmart in the baby-food section and come in canisters, and contains nothing other than whole-wheat flour and then natural fruits/veggies (they come in all kinds of flavors and my Green Cheek loves them, and one Puff makes 4 Training-Treats for him to eat quickly on the spot; he loves the Blueberry, the Apple-Kiwi, and the Sweet Potato Puffs)...So you get the idea...
So you need to train her to automatically come out of her cage whenever you open the door, that's one positively-reinforced behavior, and then also to step-up for you whenever you put your finger down in front of her legs, this is another positively-reinforced behavior....Some birds will automatically step-up whenever you take your finger and simply place it against their legs/lower belly (then reward them), others you need to do this AND give the verbal "Step-Up" command, either way you need to positively-reinforce each separate behavior she does that you desire....
As far as stopping the unwanted behavior, which for your bird is the biting right now, it's a combination of ignoring her when she bites, and rewarding her when she doesn't. They crave your attention and they hate it when you take it away. So if you're just sitting with your Green Cheek on your finger or wherever else she is and she suddenly bites you out of nowhere, you don't want to yell/scold/scream at her or any of the other really horrible advice we hear sometimes, like "flicking" their beaks, that's the worst thing you can do...Instead, you don't necessarily want to say anything, and if you do all you want to say is a quick "No Bites" in a regular tone of voice, no yelling or getting loud, and then immediately put her right down on the floor and ignore her completely...They hate being the lowest thing in the room, and they hate being ignored. You can also do a search here for "The Shunning Method', which uses the same principle but you'll find posts that explain the entire process in-detail...Basically it's nothing more than totally ignoring your bird like they no longer exist when they bite, and you reward them with a Training-Treat coupled with verbal praise when do the wanted behavior. It's an easy concept, but for a lot of people they automatically go to punishment or negative-reinforcing behaviors when their birds bite, such as yelling or scolding them, and typically that will just get you another bite, lol...Birds just don't respond to negative-reinforcing behaviors or punishment, as to them punishment is just more attention, which they crave, whether it's good or bad attention, doesn't matter at all...
And remember that at a year-old she is going through puberty right now...So something you need to make sure of is that she has absolutely NO ACCESS to any small, dark places that she can get inside of or underneath, whether inside of her cage or outside of her cage, as this will only cause more and more aggressive behavior. So this means NO Tents, Beds, Happy/Snuggle HUTS, boxes of any kind, or nesting materials of any kind (bedding, wood chips, shredded paper, etc.) inside of her cage AT ALL, if she has any of these things inside of her cage remove them immediately and never put them back in, and then ouside of her cage she cannot have access to getting underneath any furniture, behind any pillows, getting underneath any blankets or towels, etc. All of these things trigger hormonal rushes that trigger aggressive behavior, and this goes ALL THE TIME for the rest of her life, but during puberty it's just 100 times worse...