being the twin whos healthy

i find this so hard to talk about and wondered if there was many more twins out there in the same position as me? I feel so guilty a lot of the time and i’m constantly questioning why her and not me? she was diagnosed last year at the age of 30, originally thought to be just a lump she fell very ill due to high calcium levels where they discovered it had spread to her rib cage and liver. she finished her chemo a while back (and it is true it grows back with a slight curl to it!) she is now on herceptin every three weeks. though she is doing really well she deals with her situation by ignoring it as much as possible and just getting on with it, she doesn’t talk to me about it and it leaves me feeling very helpless. i am there for her as much as i can, we talk most days on the phone as i live in cornwall and she lives in our home town nearly 400 miles away.
i could say so much more, would like to hear from any other twins out there or any comments/questions anyone has. i hope by talking to people i don’t know it will be easier for me to express my feelings as appearing strong and in control in front of my family is very important to me.