As others have already told you, standard time between surgery and start of radiation is about 3 weeks. The temodar that she'll take daily during rads has to be ordered (not carried by normal pharmacies) so make sure doc's office is on that. Zofran, also--the anti-nausea pill. They'll instruct her to take a zofran about a half hour before taking the temodar--and best to take both just before going to bed.
Rads are painless, but can be exhausting, particularly in combo with the temodar, but it is the best treatment available for gbm. Avastin is second line treatment when temodar either doesn't work or isn't well tolerated.
She'll be okay. Tell her to try not to get discouraged when she feels horrible toward the end of radiation treatments. It's normal and it will get better. Be sure to talk to them about decadron (steroid) dosages during the treatment. I think many docs try to wean from the steroids too early, causing more pressure on the brain and the patient. Most importantly, stay positive and stay proactive. There are many of us doing well and living our lives with this beast.