I like that she is doing this now instead of letting someone do it later. My father had stage 4 lung cancer and they said he had about 6 months and that was about what he had even with treatments. My parents were in deep denial since he was the caretaker of my mother at the time. So saying goodbye was nearly impossible until he was in the hospital, but by then he had a stoke and couldn't talk. I wish he would have been able to give away something or mostly been able to share is memories.
I would thank her offer any support you think you can genuinely do and maybe share with her what she meant to you as an Aunt. She is grieving now I would guess.