My deepest sympathies on your unexpected loss.
There are a number of things that can cause a sudden death like this.
It could be she had an undetected heart issue, or if she was not on heartworm prevention that parasite could also be the cause.
She might have had an aneurysm that let go causing sudden death or a blood clot that lodged in a critical location cutting off blood supply or a tumor on liver or spleen that ruptured causing internal bleeding.
She may have had an allergic reaction called Anaphylaxis perhaps from being stung by a bee or wasp.
An epileptic seizure can sometimes be fatal depending on where in the brain it hits.
And difficult to detect health issues such as Addisons disease, an adrenal gland issue, can also cause sudden collapse and death.
The only way to know for sure what cause of death was would be to have a necropsy done of the body by a vet to find cause of death. Its like a human autopsy.
The loss of bowel control and the emptying of bladder and bowels is normal when death occurs as the muscles holding the sphincter valves shut let go and if waste materials are present they are expelled from the body.
If you have not seen www.petloss.com and the rainbow bridge story it may bring you some comfort.
Hope this helps you!
Dog Expert:Rescue, Train,Breed,Care
30+ yrs dog home vet care & nursing, rescue, behavior&training, responsible show breeding, genetics