I'm sorry PT52 - We'rea ll here for you. I think it's as much of a blow for your family and loved ones, as it is for you when you are first dx'd. I'm sure they want to help. You'll show them over time how much stronger you've become. You are a strong person, and don't need to base your happiness on purpose on what others think of you.
Give your sis as much literature as possible - I find it too painful to try explain to someone, especially if I get threatened with the "Well, just snap out of it" kind of answer