Help what should I do, all the rules are different!

I feel like I have stumbled into a strange world, through circumstances of life,work, and distance I have become a primary care giver to my sister in law (the wife of my husbands brother..)who I must admit over the serveral years we've been family there has been some underlying resentment on her part made worse by her first bout of cancer which put some more distance between us (as she put it "sometimes it seems the better your life gets the worse mine gets) The really wonderful thing is we got through all this BS and have become really close, she has had a really rough go of it with her meds and sickness and friends and kids and husband that sometimes happens when your world is devistated- her diagnosis this time aroundis terminal and although they gave her 3months and she is going on six but with the end seeming to close in she has yet to begin work on one of what she has discribed as her most important gifts audio tapes to her children- she says she wants to do them but each time its brought up she gets very emotional and doesn't want to deal with it that day, given our history I don't want her to feel pressured by especially me, I don't what her to feel alienated when our relationship has become so important but at the end I don't want her to have that regret, should I encourage her?