Sister troubles

I have a half sister who hasn't had contact with my family for over 10 years. I don't know her reasons but I really want to meet up with her and stay in contact. I wrote her a letter and forgot to send it, and I've just found out she has been diagnosed with a life threatening disease and soon won't be able to walk again. Should I send the letter still? I'm worried she will think I'm contacting her because she's sick, but I'm contacting her because she's my sister. What would you girls do?