I am so sorry for your loss. I know it's painful. I am sure you were an excellent mom and you did everything right. You'll probably never know exactly what and why it happened. I've heard too, that when the mom senses that something isn't right, she'll dispose of the baby. Or maybe she was trying to move it and accidentally punctured it. I am so sad for you, tho.
I am sending ((((((((((((hugs))))))))))))))) from me and Spencer. As far as whether or not to breed her again, it's a decision that you'll have to make. My opinion is, I would try to breed her again and see what happens. If this was her first litter, she may have just not known what to do....sometimes they don't have that maternal instinct. I have a maltese and she had a little a few years back. If I would not have been there, she would have killed them all. She had no idea what was going on. I had to basically "deliver" the puppies and show her what to do. After a few days, she was a great mother. But again, this is just my opinion.
Good Luck in what ever you decide. We're all behind you!