I'm sorry to hear of this with Bella. I have advanced training in feline behavior and I need to preface my discussion by telling you that feline aggression toward the owner can be challenging to manage. Many cats display aggression toward their owners when displaying assertiveness. Cats that have this type of problem usually display a confident temperament. They exhibit assertive or status aggression by biting or threatening when the owner attempts to approach or handle them or to simply show their displeasure or anxiety with their place in the hierarchy in your home. The bite behavior may be an attempt to control these situations. Assertive displays, pushy attention-seeking behavior and attempts to control the environment by blocking access to doorways and refusing to be moved from perches or sleeping areas may also be displays of social status. One sign that might signify this type of aggression is aggression toward members of the household that a cat can control (you), avoiding aggression with family members that control the cat and do not routinely give in to its demands. The prognosis is guarded as these cats may be dangerous and the problem may have both innate (Bella is likely to have been feral as a kitten) and learned components (she may not have been socialized prior to the important age of 7 weeks). Too many of my owners have ended up hospitalized due to cat bites. You must decide whether Bella's risk to you is warranted vis a vis attempting to manage her inappropriate behavior. If you're willing, management involves the following:
Make the situation safe - identify stimuli leading to aggression - avoid confrontation and any stimuli or interactions that elicit aggression - teach simple commands such as "come" or "sit" by using food lures whenever Bella is receptive to food or play.
Withhold rewards unless earned - Bella should be taught to defer to you for any treats, affection or play. For instance, play, affection and treats should never be given on demand but can be given if she responds to a command. After a few weeks of teaching deference, she can be taught to accept stimuli that have triggered aggression. You would need to begin by performing a behavior that has triggered aggression in the past but in such a muted way that no aggression is elicited. If no undesirable behavior is exhibited, she is given a very tasty food reward or play. Once she's conditioned to accept a mild level of the stimulus, the sessions can progress with stimuli that very gradually become stronger.
Punishment must be avoided but undesirable behavior can be interrupted with alarms or a can of compressed air. Care must be taken with this approach since some strong stimuli can make a cat more aroused and aggressive.
Uninhibited aggressive displays that appear impulsive, explosive or excessive may be reduced with psychotherapeutic drugs - SSRIs - such as paroxetine (Paxil) or fluoxetine (Prozac). I don't favor this approach for what, in essence, is normal behavior for many cats. Drugs, however, are an important resource for the determined owner.
As mentioned above, Bella is a significant danger to you and others to whom you might rehome her. If you're highly motivated to keep her in your home - and I understand that you're likely to be fearful of your own pet at this time, I would suggest your seeking council with a board certified veterinary behaviorist who will come to your home and examine the dynamics therein. Bella's vet should be able to refer you to such a specialist or you can find one here: www.dacvb.com. I like the idea of keeping her sequestered in a quiet and dimly lit room as needed until her level of arousal abates or perhaps making her a mainly outdoor cat - where she needn't socialize to an extent past that which she's amenable.
Please respond with further questions or concerns if you wish.