I am a college student and I just dealt with the death of my father from GBM IV on January 22nd. He only lived for 5 months after his diagnosis despite surgery/chemo/radiation/Avastin. I took care of him the last two months, and I know how hard it is, but you'll be amazed how strong you can be in such a tough situation. Many people, including myself, felt a great deal of peace when it was finally over. I'm normally not a religious person, but I truly feel my dad is around me at all times now - urging me to go on as "great things are about to happen."
Several days before death, the GBM patient often falls into a continuous state of sleep. When the "death rattle" starts, that normally means they're really close to the end. If you're using hospice, request an atropine patch if they don't provide it, as that makes all the difference near the end. It will stop any secretions coming out of her mouth and reduce or eliminate the raspy breathing.
The patient's hands and feet will start to turn blue, though in my fathers case that went away following the atropine patch. Then the breathing will be broken up by brief pauses - for only a second or two - and then eventually they'll pause but not return back to normal respiration. Then hospice comes and verifies they have no vitals, and within an hour or two she'll be picked up by the crematorium or morgue.
I am only telling you because I so desperately wanted to know what to expect before my father passed. I was terrified of those last moments for months, and yet when it happened, I was somehow okay.