I dont know if it is possible but does anyone know if a snake can drown in its own regurgitated fluid?
Also its unfortunate but snakes are exotic animals and sometimes they just plain succumb to stress and in her condition she might not have been able to handle the move to a new home on top of her poor health...
Make sure to thourougly clean with disinfectant (preferably bleach) anything that may have come into contact with your snake, that way you will not spread anything to any other snakes you may have or get in the future.
I am sorry about your terrible loss, but I am sure the snake was more comfortable with you in her last moments than she would of been with the original owners.