is it possible she has a heart condition or an anyuerism, and the bruise occurred because she fell, and the scratched occured because the 2 year old had tried to wake her up?
there are a lot of tings that can cause sudden death.
also, she may have had a slight fever or pain and not mentioned it. or it could have come on quickly. but quickly enough to not be able to call 911...??? hhhmmmm.....