My dog killed my little dog, what to do?

A couple of days ago we had a tragic incident in our home. We are a family with many dogs and some are small (Chihuahuas) and some bigger as my bitch who is 30 kilos of pure muscle.
The kids where playing having all the dogs inside our camping wagon. The dogs where in the bed and when the kids went to the house to pee my big bitch attacked my dearest Maja. I found her lying looking dead, lifting here up and the only thing she could do was move her thounge. I think her back must have been broken from the weight of the big bitch. She died in two minutes, giving me now time to go to animal hospital.
The kids where crying and my daughters friends wanted to go home.
I never let the bitch back in the house, she is staying with a friend of mine until I figure out what to do. I want to put her down if she is dangerous to other dogs, but what if it was an accident, that she used her legs to push Maja and her back broke? Could she maybe stay with someone that don't have Chihuahuas? Or is the safest thing to do to let the vet put her to sleep.
We lost two of five dogs that day, they are all like family to me and my daughter and the whole incident was and still is a tragedy.
What should I do with the big bitch?