Oh goodness. You have my sincerest condolences. Unfortunately, there's not much a human can do to catch up to a dog, and no amount of reasonable foresight could have stopped it. There was nothing more you could have done.
This makes me appreciate my family's golden retriever that much more. Think I'll go give him a pat. May your dog frolic in her happy place forever.
Cherish your pets while they're still here, because you never know when life will decide to take them away...