If she is whimpering, she is in pain. If it is terminal, then you are just prolonging her suffering to make yourself feel better. I think everyone waits too long to put their dogs down and I used to do the same before I realized I what I was doing.
It's always very hard, but I have learned if their quality of life is not good, then it is time.
I don't have kids, my dogs are my kids and I hold them while they are put to sleep.