karla,
it doesn't matter if they're 10 years old or 100 years old. if they have a blood disorder or they react badly to an operation. whatever. it's never the right time for us to lose them. as long as suzy is comfortable, and you're offering her what you can to eat and to comfort her, try not to feel too bad.
easily said, right?
there's nothing else to be done. i feel sorry for shimano, who will miss her sister like crazy when this is over. try giving her some extra attention.
when my cat was sick, at the end, we poured our love into tenzing and poor shuju felt left out. afterward, she wouldn't let go of us for a minute. i still feel bad about that.