Dog Acting Aggressively Since Having Puppies?

My seven year old dog got pregnant at 6 1/2 yrs old for the first time. When she went into labour there were complications and she had to have surgery. She lost five, ate two and the lone survivor lives with me as well. She has not been herself. The pregnancy and the child raising and surgery were very hard on her.

I thought she was not going to make it, however she recovered and started showing signs of her old self, but her temper and attitude has changed. She has become aggressive with other dogs and other people, she has growled and nipped at one 13 yr girl, even got her leg with a tooth. She had shown signs of not liking the child and her siblings, they were scared of dogs, especially the younger child in the family! I kenneled her right away and told she was bad! I thought it was due the way they acted scared, I have been keeping an eye on her, so far nothing again until today. A girl who was here earlier, a family friend, went home to eat and do chores, she came walking up and the dogs barked to tell me she was there, but then my dog did not stop. I told her to say hi to the dog let her hear her voice and she snapped at her, and got up and tried to get her again, as I was already running to grab her! She was on her lead so she could not. I put her straight into her kennel.

What can I do? What should I do? A muzzle?
I do daycare for a living and I have two of my own children, she was not always like this, I am sad at the thought of having to put my baby to sleep cause she is dangerous!

By Michelle R