E.G.
J.,
I truly understand what you are going through and how difficult this is. I am not going to tell you anything that you do not know, but right now your heart, not your head is ruling your thoughts and actions, so here goes...
You said your mom is a fighter and she has been fighting, but it appears her time has come to move on. You also said sshe has always been there for you (holding your hand throught child birth) and she will always be there for you and with you - even 'holding your hand' when you give birth to your next child.
I know you are feeling selfish and anticipating the pain of not having your mom physically with you, but she understands this is her time. The most loving thing you can do is to sit quietly with her, tell her all the reasons you love her, and let her know that it is OK for her to go - you will always love her and carry her with you. You and your children are a precious part of her legacy.
With 'love and tears'
E.