As to the how - obviously childbirth is extremely strenuous on the human body. Under the strain, she could have blown a blood vessel in her brain, developed a clot that caused an embolism, or any number of other causes of sudden death. Current medical practice would not be able to do anything.
That’s sort of an inherent risk to being a fragile creature made of living meat. I’ve expressed my opinion a few times around these forums. Her death may have been inevitable, but we as a society did not need to guarantee it was permanent. If she died in a hospital, her brain could have been carefully preserved by licensed professionals, and as soon as we develop the tech far enough, she could be brought back to the living through some form of emulation.
There is no scientific evidence to say you cannot do this : all credible knowledge as of 2017 says that if the information was in fact preserved, she could have been restored once society has the means to emulate brains from that information.