A Lucky, Lucky Girl Indeed...
That said, when I told her my situation, she was so wonderful. First she was adamant that no, they were not taking back their offer. She said I can certainly defer for a year if I need to, and also that she is going to talk with some other people and find out if there is any other form of alternative funding available so I don't have to count on the TAship for the tuition waiver for the first year; I might be able to take classes and work in the writing lab instyead, then TA the following year, for example - she doesn't know, but she is going to explore options and get back to me. I felt so relieved to hear that this is not unusual, that they do make exceptions, and that there are precedents for this (See? Always ASK!) It would have been so much easier for her to just say "Well, thanks for the heads-up, appreciate you letting us know before April 15, apply again when you're clean". Instead, I was re-affirmed all over again a.) that I certainly chose the right program to work in and b.) I'm worth it.
SO...Cancer, yes. Cancellation of PhD - NO WAY!
I am a really, really lucky girl, all things considering. OK...off to sleep off the next round of Vicoden.