Your mum sounds like her heart is failing. When it goes, no matter what you do, the body will not respond. And when people get older, their bodies in general break down. The vomiting and fainting and diahrrea can come from being dehydrated, which is why they gave her saline. Sometimes if a person is anemic, they will give a transfusion. The swelling that took place is likely because of poor circulation. People who spend a lot of time in bed will sometimes faint when they stand up, which is the blood pressure thing. Older people sometimes take a lot of medicines, some of which can also affect the blood pressure.
Since your mum has been like this for more than a year, I think she is likely giving out. This is the natural order of things, but I am sorry to hear she is feeling so sick, so having a word with the hospital chaplain will help you with this. You may also ask the doctors to give her medications to keep her more comfortable.
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Ya, it sounds like nothing else they can do. Don't think the worst. She had a long live. She sounds like she is deyhdrated try to give her lots and lots of water. Im so sorry you are doing so much for her and you can do anything else. My grandpa is not doing so well either. He's 90 I look at it this way he had a long life and I don't want him to suffer I rather him be in peace. Take it one day at a time. Just remember god takes the best.......