Feline hepatic lipidosis (IE fatty liver disease) is the most common liver issue that adults cats face. It is most often seen in an older cat, and is usually caused by the cat losing too much weight too quickly, or by kitty being deprived of its food for even just a few days. It can be secondary to a viral infection - say, kitty gets a cold, and won't eat for a few days, and that may be enough for the liver to start shutting down - or it may be secondary to something else, like diabeties, Irritable Bowel Syndrome, or hyperthyroidism.
If caught extremely early, it is sometimes possible to reverse the progression of this illness, with constant and consistant force-feeding, administration of subcutaneous fluids twice daily, and slow encouragement towards weight re-gain.
There is really so little known about what can set off this disease in cats; I am sure that you could find an article out there that would say it could have been sparked be her innoculations, or even just the stress of the vet trip. But, by keeping her up to date on her shots, you were helping to keep her safe from oh so many other things!
I am so sorry that you lost your baby.
10 year small animal specialist