(I'd say I'm sorry, but I don't know you, her, anyone around you and I although it's bad, I can't really make myself feel anything).
In short. You're not the one that's dying, it's just not up to you. Let her do whatever think it's appropriate (telling her anything about it would be just imposing), and keep your own memories, however you want them (blog probably, although your head would suffice). Don't overdo it - otherwise your risk killing parts of you and your daughters in the process.
And, you seem too depressed to ask on Slashdot. Please, please, please, talk to someone, even a professional (even with the related social stigmata related to that). Don't try to offload this on a bunch of strangers, that's not going to work well anyway. We suck. Even though a lot of us lost someone dear sometime ago (me - about a week ago), it still doesn't make us any good in offering good advice on anything like this.
Seriously. Please 1) don't be an idiot 2) do what's right instead of using strangers to thing for you. Yes, you might fuck up, so what? You'll still remember her for what she was.