I am so sorry to hear she is beginning to give up, but she, too, must be aware this is the end of the road.
She may liven up tonight and be her bright old self for a little while.
Three of my cats came to say googbye to me this way, they managed to pick themselves up enough to make it a proper, intense and emotional goodbye, and I never understood how they managed to do so, sick as they were......
With Tuppence, I wasn't even aware she was that far gone, I went to the vet to have her treated, but had to let her go, instead.
Like you say, we can help them live a bit longer, but is it really worth the stress of sticking needles into them or forcing pills down their throats?
It is so very hard to let go, but Ollie deserves to journey to the rainbow bridge with feline dignity.
Wish there was something I could do, but there is nothing, besides thinking of you, feeling for you, crying with you......
But I am sure Ollie knows how much you love her, how intensely you will miss her, and she will be ever so grateful to you for letting her go when the going is still good, or at least bearable.
Cats understand, Ollie will understand what you are doing for her, and what it will cost you to let go. And she loves you all the more for it.