I agree with several already who recommend fabric designs or patterns of thngs that maker her feel safe, connected, "filled" with things that make her happy or centered. In the period of three and a half months our guild had eight members diagnosed with breast cancer; our guild also has breast cancer survivors who were an immeasurable source of strength and hope and recovery to these ladies, my friends, our "sisters of the cloth." All of the survivors shared they wanted nothing to do with pink ribbons until their first anniversary of survival - I'd keep that in mind for sure.
Another thought - since the process is five years, I'd think about five borders (or six, for that 1st anniversary) and maybe think about appliqueing little things in each border as that year-in-progress is happening, maybe it could be appliqued while the chemo is going on as you sit with her. I am a firm believer in holding the space for what can be, and creating a quilt with five or six borders does that. BUT each recovery and patient is different, so I offer these ideas with many prayers for your sister's success in the years to come.