Simon,
What form of big 'C' have you got? Not that it changes the fact you have a fight on your hands, just puts it in perspective.
I had a dose of skin cancer a few years back. Thankfully it was 'only' a BCC, but scared the bejesus out of me. Once bitten twice shy I can tell ya.
I would like to say "stiff upper lip" and "look after yourself", "stay positive" etc, but as you know, from a complete stranger, it dosn't really help. Instead I will say this....
Trust your doctor, eat well, don't binge drink, know that people do actually understand.
And... she'll be right mate.