Naomi
as I was reading this, I thought wow she really did explain it very well to you...because it seems to be explained so well in your post.
the first thing I wondered about it, was the 30-50% success rate.
you need to know, does that mean 30-50% as in her chances of making it THRU the surgery?? or does it mean her chances of the surgery helping? be very sure to find out what the chances are of something going wrong during a surgery like that...I don't want to scare you, but it is something to think about. that sounds like a extremely serious surgery! but she is only 4 yrs old(right?) so I would also be leaning toward wanting to have the surgery done on her if she were my cat.
also, can the vet give you information on other cats that have had that done, or do they know of anyone, maybe other vets have had patients with that disease? try the universities, maybe they have info on it. vet universities etc.
and, after the intensive care, how long til a complete reccovery?
will she be able to do normal activities and play after she is recovered? is there any known downside to life after the surgery?

that's all I can think of right now, but I will let you know if I think of anything else. you have SO MUCH to think about and so much worry, can I help you in any way, like with find/gathering info from universites and the interent? PLEASE let me know, I would be glad to .