Dog died, cause of death..?

You should have a necropsy (autopsy) done to actually find out the cause of death. I don't think a dog would intentionally drown itself, unless they dog already knew she was going to die. But it does sound weird for her to bleed from the mouth, unless something had erupted from an underlying condition. I know it's hard to lose a dog, mine had died out in the woods back in '02. She was 15 yrs. old. My prayers are with you.