I'm so sorry, what an horrific tragedy. It's painful enough losing a pet to ill health or old age but to lose a youngster this way is heartbreaking.
I see the member who lost her pup has contacted you. She will be a shoulder to cry on having experienced similar and I know she will be very supportive.
In the meantime, please don't beat yourself up, it's something that can happen to any of us.
I'm heartbroken for you.
RIP little Angel.