My wife and I have counseled a number of people with serious health issues and incapable of work. We've always been appalled at those that could be on social security disability but never went to the doctor regularly and had a paper trail required to use their benefits. There's no substitution for someone taking care of their own healthcare.
To get on Medicare, you've got to have 40 quarters working and paying into the system. That essentially means 10 years of gainful employment. After Social Security Disability deems someone disabled, Medicare starts 2 years from the starting date of disability. Young adults and those chronically unemployed in bad health end up on Medicaid, but they find it very difficult to find quality healthcare with doctors often not accepting it.
When it comes to end stage renal failure, most likely the person will go on hemodialysis. Nephrologists may try to talk patients into going on peritonial dialysis, but it takes a strong, young person to handle flushing themselves out with a tractor trailer load of liquids monthly.
Best thing you can do for your sister is help her get all her legal ducks in a row--including a will and healthcare power of attorney. You could also assist in getting paperwork filled out and filed for Social Security Disability. It may be of some assistance. So often, those in such bad shape cannot handle such details on their own.
If her liver is in such bad shape, it doesn't sound like she has a good prognosis. We're so sorry.