Anticipatory grief

In the immediate term, you understand much more, so you will likely grieve much more strongly. For them if they have any concept, the situation at hand is normal. You know what is coming, just like I do and so you cant feel selfish for grieving. She probably doesnt want you to see her like this, probably doesnt want the kids and husband there either but knows she has to. Shes still talking to you which shows she most likely wants you to remember her as she was and not how she is now. She probably feels she is protecting you.

Just be there for her in what ways she allows, grieve and dont feel selfish, in situations like this we have to be a little selfish or we will go crazy.

Thank you so much for your reply. I think she has been processing this moment for a while. I know she's had a lot of counselling etc.
I'm playing catch up and I wish I could change her outcome as she is incredible. Thank you.

Yeah even before the diagnosis my dad has been thinking it would happen. My sister said that people sometimes know even before they find out for sure. My dad is yet to be fully diagnosed with his primary tumour, so we dont know how long. 

I would imagine that your sister has gone through all the stages and is now at acceptance. We always find a way to shield ourselves from the absolute horror that is knowing someone you love is coming to an end, and when it hits us its almost like we suddenly realise how important they were and we begin grieving even before the end has come. 

I think counselling would be good for you, I would ring up Macmillan and talk to someone, which I intend to do myself at some point. 

I wish you all the best through this, you're not the only one going through it.