I am so sorry to hear what you are going through. I was dealing with the same feelings few months back. My mom, my true friend was diagnosed in Jan. 08 with Bile Duct. She spent wonderful moments with us till Aug. 23 rd.
It came as a shock-her diagnosis, because at 70 she had more stamina than people her age.Now I am trying to come to terms with this reality. I have to accept it, there is no other way.
All I can say is, you have to be STRONG. This is life, its temporary. We all will leave this world one day...this is the true fact of life. Face it, come to terms with it. There are people who die in accidents all of a sudden.
Atleast, with this disease God gives us an opportunity to prepare ourselves.He gives us a chance to pray for our loved ones- and believe me there are Miracles in some form or the other.He gives us a chance to take as many pictures and memories as we want. To say all that we want to, to hear all that our loved one has to say. A chance to keep them happy, to fulfill their wishes.
God gave me this chance and I will always be thanking Him for that.It is because of our prayers that my mom did not suffer. She went so peacefully in a way that many healthy people don't get to go.This gives me peace.
Each of us has to go one day, so make yourself strong for the life ahead. You do not know what lies ahead. Pray and find the peace in it. Keep your mom happy, you never know God might show his miracle to you and your family. Pray that she stays comfortable and does not suffer.
My best wishes for you and your family.