First off, let me say that I'm VERY sorry for your loss.

I would suggest reading our Care Sheet for help in preventing future unexpected losses.

When an animal (or a person) dies and lays in one position for awhile, the blood will pool at the lowest point of the body. That is probably why the bellies looked so dark and red. I don't know about the fluids, but am hardly an expert on such things.

I fully agree with the others who suggest taking your remaining snake to the vet. I'd also get her into a new enclosure with all new bedding and "furniture", making sure everything is clean and sanitized. And once again, refer to our caresheet to be sure her environment is optimal for prolonged good health.