I'm sorry that your question wasn't answered in a timely manner. I have advanced training in feline behavior and must tell you that there are a quite a few considerations in these situations. I'm going to post my synopsis of aggression toward the owner below but because Daisy is 14 years old there are additional considerations not mentioned in the synopsis. The most important of those considerations is pain aggression. At 14 years of age, certain medical disorders - osteoarthritis, renal and hepatic insufficiencies, e.g. as well as hyperthyroidism, inflammatory bowel disease and neoplasia (cancers) are more common than in much younger cats. Because Daisy's change in behavior is recent, it would be prudent to have her vet perform a thorough physical exam including diagnostics in the form of blood and urine tests. There is also idiopathic (unknown cause) aggression which is unpredictable and appears to be unprovoked. It's been described as "toggle-switch" aggression insofar as it may start suddenly, as if a switch has been turned on. At Daisy's age brain tumor needs to be considered to underlie such aggression but a tumor would remain conjecture unless identified with MRI. This type of aggression is difficult to treat using standard behavior-modification techniques because it's unpredictable.
Here's my more general synopsis:
"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 (she may 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 Daisy'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 Daisy is receptive to food or play.
Withhold rewards unless earned - sheshould 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 prefer not to prescribe these drugs for what, in essence, is normal behavior for many cats. Drugs, however, are an important resource for the determined owner.
As mentioned above, Daisy is a significant danger to you and others to whom you might rehome her. If you're highly motivated to keep er in your home, I would suggest your seeking council with a board certified veterinary behaviorist who will come to your home and examine the dynamics therein. Daisy'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 until her level of arousal abates or perhaps allowing her outside more - where she needn't socialize to an extent past that which she's amenable."
Redirected aggression needs to be considered as well. This occurs when the target of Daisy's aggression (you) is not the stimulus that triggered the state of aggressive arousal. Territorial, fear-induced and defensive aggression are the types of behaviors that are likely to be redirected by her. Stimuli that can cause an aggressive state of arousal include the sight or sound of another cat (at times quite far away from the home), unusual noises, odors of other animals, unfamiliar people, and unfamiliar environments. A common situation is one in which the pet becomes aroused upon seeing or hearing another cat while sitting in a window. When the owner attempts to pet it, pick it up, or nudge it away from the window, it attacks. It may show aggression toward another pet when approached in similar situations. Redirected aggression is a common cause of the sudden appearance of aggression between cats in the same household that have been living together amicably for quite some time. This type of aggression is probably the most dangerous type of aggression cats exhibit due to the uninhibited nature of the bites. Treatment involves identifying triggers for arousal and then removing the pet's access to the stimuli. You may have to be quite the detective as stimuli can be imperceptible to owners. Medication can be beneficial for reducing Daisy's response to environmental stimuli - psychoactive drugs such as Prozac have been used. The most important thing that I can impart to you is to be careful around Daisy when she is aroused. Too many of my owners have ended up in the hospital due to infected bite wounds. One encouraging fact is that many of our cats will habituate to the arousing stimuli and "self-cure" within weeks to months.
Please respond with further questions or concerns if you wish.