['My sister just passed away.', "Wow, That's unfortunate. Sorry to hear. were you close?", "We were, it's so tragic. Cancer spares no one.", "I hope you are finding ways to cope with your loss. That can't be easy to deal with.", "It really is difficult, I've started therapy recently."]
I hope that helps you and that you find peace.
When my sister passed away from cancer. She had been diagnosed 3 months ago.