Well since I'm not there to see it. I can't say if she's going "after you" or not.
But in her own mind she might be trying to play with you, some cats play very rough unless they know otherwise.
Another possiblity, is that Alpha cats (which she seems to want to be) like to break up play sessions or fights, specially with other animals or people who are doing it in her territory.
Any GOOD animal rescue will understand this cat and how to take care of her. A cat suddenly getting tired of being petted is very common, and their owners need to learn when to stop ahead of time. Any GOOD rescue would not put an animal down for this type of behavoir.
If anything a foster home free of other animals through a rescue organization would try to work with her and help her behavorial skills until she found a perminate home.
There is also the option, that since she is so old, and obviously stressed enough, the she would be placed in a home as an only pet and allowed to do what she pleases, cats don't have to be petted, they can have nice companionship by being fed and talked to. Trying to "change her ways" at this stage, might do more harm then good for her old self.
I personally, just from working with many cats like this. Feel that it would be better, to rehome her to a nice quiet place where she can be the only animal, would be a better alternative to giving her rescue remedy every day, or getting some prescription medication from the vet that she would stay on for months or life long IF the vet deems this to be behavorial as well.
One of my cats Asim, has a similar problem, we've tried the medication route with him, and it was not pretty. He was so miserable, not the same cat anymore, he sat around in the dark half a sleep and foaming from the mouth sometimes, because he was so "stupified" as I call it, from the medications we tried, I was miserable, so I decided to stop the medication and give him my time, love and understanding instead, and it has worked out for the best. Asim tells me when we have reached his limit of strange activies or new animals in the house, once we reach that point I get rid of any of the stress factors.
Like say I'm fostering a dog, if it bugs Asim we stop fostering for a while. You however don't have the option of getting rid of your dog or cat as they are perminate. You could however, give this cat a nice quiet peaceful place to live in someone else's home for the rest of her days.
I'm not saying your a bad cat mommy, it sounds like you have tried and that you are still trying. I just personally think the rehoming alternative would be best for all of you, based on the info you have given us here.