Aggie, please cry all you want. I got tears in my eyes just reading your post and my grandmother died in 1976. I was 26 years old at the time, but I felt like throwing a three-year-old tantrum. I still do, for that matter.
Don't worry about how your reaction differs from your mom's. As Lisa pointed out, age and life experience affect how we experience these things, and your mother may well be projecting a calm exterior regardless of how she feels inside.
The loss of a loved one is painful and frightening, and illness reminds us that these losses are inevitable. There's just no way around the awful feelings; they are the price we pay for knowing love.
I'm so glad to hear that Mammaw has dodged this bullet, and I hope she is with you for a good long while.
Pam