Training Maggie

We adopted Maggie a little over three years ago. She is extremely spoiled, but we think that she deserves to be a "tad" spoiled because she belongs to us.
We had only had Maggie about three months when my daughter came to visit with her four or five children. Maggie snapped and snarled and had a nervous breakdown while they were here. Well, I didn't snap or snarl, but I did about have a nervous breakdown. I was so terribly worried that she would bite one of the little ones. My daughter wanted to take her for a walk, well she would have none of it!! We finally had to kennel her to keep her from doing bodily harm.
Well.....today we had my son's family for the holiday. Day one with two adults and three little boys; full of energy, running, jumping, yelling etc. Once again, Maggie was snarly, snapping, barking non stop. Once again, I was about to have a nervous breakdown. Once again, Maggie was disciplined, put outside on a run etc. Day 2: Maggie laid at my feet, watching the boys go through a test of activities for her to judge which ones she would go out of control. These activities were set up by my son, because he couldn't believe she could change over night. I told him I thought she believed she might as well get over it because they were going to stay all the time. Not once did she growl, bark, or even got up on her feet. She's such a good little girl.  lol