I am so very, very sorry for your loss of your beloved cat, and I feel from your post, that you truly loved her as a family member. It is so hard to see them suffer and then lose them when we love them so much. But, at least she is no longer suffering and you did do the right thing to put her down when her quality of life was deteriorating so badly.
To answer your second question, first, your cat sounds like she was quite ill, and since she had so many different symptoms, there are numerous diseases that she might have had. The following website tells about Chylothorax, which is treatable, but can be fatal that affects the lungs of a cat.
Also, since she had such high blood pressure, she might have had something rupture, such as an aneursym, in her head, or lungs, that could have caused the bleeding. You did not say what anxiety medication she was on? Was it perhaps valium? There are now some vets that will not treat cats with valium, as my own vet told me it can "blow out the liver" in a cat. I think he met, that it is very dangerous for some cats, especially to be on it long term.
She could have had a blood vessel rupture in her esophagus, that could have caused the bleeding. There are really a lot of different symptoms and diseases that can cause these symptoms in cats, as well as in humans. It is just a matter of guessing at this point. I am not a vet, but I do read and study quite a bit on the medical aspects of animals, and I have been dealing with many different acute and chronic diseases in my own cats and dogs over the years.
Did she get checked for FIP if she was young? Or FIV? I have a cat now with FIV that I am always keeping an eye on, as I lost one of my other cats, two years ago to complications of the FIV. He was about 13, and he was extremely anemic and could no longer swallow, as he seemed to have a tumor in his throat, or severe gastritis. But, I did not want to put him through any testing that would cause him more pain, and we had him put to sleep here at home.
She could even have had some kind of neurological disease that caused the swelling and bleeding, and trouble with walking. FIP will sometimes cause these strange symptoms. I was wondering how old she was?
God bless and take care. Perhaps one of the vet's or technicians on the website here can give you some answers about your kitty.