Problem with an aggressive cockatiel?

Right, I have a rescued cockatiel and she is very aggressive, I know it isn’t her fault so don’t get me wrong. I have spend a long time trying the gentle approach, treats and talking to her every day and not invading her space and all the stuff the websites and care sheets tell me to do, and it isn’t working. Now I know some of you will tell me to be patient etc BUT it comes down to the bird being dangerously lonely. She can’t have proper human interaction cos she bites, HARD, she draws blood if she can get you, which she does, even when you are changing her food and water. Due to that I dont trust her enough to introduce another bird for company. She needs interaction of some kind, no creature should be alone. She barely moves off her perch, doesn’t play with toys etc. I need real help with how to deal with this, not the same stuff I get off care sheets and the like. Is forced handling (to a certain extent) an option, maybe it will teach her I am not going to hurt her, but maybe it will stress her. I am used to small mammals, so this is difficult for me to know what to do with a bird. Sorry for the long question but the details are important. Thanks.