I had proton beam therapy in Liverpool last year at age 34. Is that where she has to go too? If so there's quite a lot online to read should you wish to scare yourself silly
Clatterbridge clinic
To try and answer your questions:
treatment for me (front of eye) was :
trip to Liverpool to see the consultant Mr. Di Mato to have all kinds of eye exams done - including a none too pleasant ultrasound of the eye.
another trip (Clatterbiridge) a few weeks after for the mask fitting
a week long trip to Clatterbridge, staying in a hotel which NHS pay for - being strapped bolted into a scary electric chair type thing with a nasty mask over my face and mouthpiece in, being zapped for a minute a day for a week.
3-6 monthly checks - got my next in August after 9 months break and hoping to be signed off.
Only side effects for me as very sensitive to light/wind and a bloody great big floater that distorts my vision.
I believe in the back of the eye that they operate a few weeks before the PBT and put "markers" into the back of the eye, to presumably stop rays hitting brain, but not 100% sure.
Yes curable, yes may be benign, can be aggressive, can be not. Helpful I know sorry
CAT me if you like, I also have a few photos during treatment.