My very best friend in the whole world just went through this. She spent a lot of time in the hospital and then just chemo appts....she was 25 when it happened. i'll ask her more what she did, but here is what I know off the top of my head.
movies, reading, started knitting, learned to sew, wrote cards/thank yous, artsy/crafty things, games, cards...loved visitors when she was allowed to have them!!!!! They set up a website for her where people could write...she loved reading that! I wish your cousin the best of luck. fyi - my friend is on a chemo pill (it has been 1.5yrs) and other meds, but it looks like she is cancer free! :) I'll be praying for your cousin!