Anniemay,

Hi, I'm not too far from you. Is Syracuse where your sister is being treated too? I'll just repeat what everyone else has said here,

First, help her get adequate pain medication.

Second, her anger may be covering up depression and/or anxiety as well as being a result of the pain. There should be someone she can see (ideally a psychiatrist) who can prescribe some meds to help her mood a little.

Third, make sure she is getting adequate nutrition, hydration and rest as all three of these can affect her emotional state as well as her ability to take the radiation.

p.s. if your sis is in Syracuse, I have a friend who is a psychiatrist there who saw me in the midst of my treatment and knows how rough this is.