She is exhibiting typical stray/feral behavior. First off, stop presenting yourself the way that you are to her with your hand offered in her face. If you can approach her, do so and reach out and pet her back first. Watch her for signs she will attack you- if she is going to attack, her ears will go flat, her tail rigid and she will turn and strike quickly. If she bites you (and it sounds like she will) don't move your hands or fingers quickly.This simulates prey to her and she will go deeper into the object in her mouth (either her claws or teeth) instead scream once- a short burst to show her she has hurt you. She should withdraw.
Buy a bottle of Feliway Spray- spray a washcloth until damp- wipe down all your cats with the same cloth- spraying the cloth between each cat. Wipe her down last with the same cloth. Take and spray her at the base of her tail and between her shoulderblades after you wipe her down.
Buy Rescue Remedy and start putting it in the food (wet food) or add it to the water.
Also, be careful of those scratches and bites, they can become infected quickly. Make sure you wash it out well no matter how minor you think it might be. Use a betadine scrub and then an antibiotic ointment. Leave it open to air during the day and cover it at night if it is deep- but remove the bandage in the mornings.
Good luck with this cat and thanks for opening your heart and home to her.