Vets can be hesitant to advise putting the animal down, so if/when they say it in as many words then listen. Using phrases like end of life care is a definite hint that you should be asking the question you're asking.
although it never hurts to get a second opinion. some vets if they also cater to livestock can be a tad gung ho when it comes to pets.
Obviously you know your animal better than any random stranger on the internet, and i'm not wanting to sound condescending but i do need to ask if she's just hiding pain. Its truly insane what animals can tolerate without showing it, guess its a survival instinct never show weakness or maybe they just dont feel pain the same as humans do.
The scary thing with cats is they have a tendancy to know when its time, and they'll go off to find somewhere quiet to die, and you do not want it to get that far.
Whenever you make the call, and it sounds like if it isnt now then it isnt far off, stay with her, dont let them take her off to a back room, folk suggesting a home visit is even better if its an option.