This prosecution makes no sense.
How can she be charged with kidnapping, but not murder?
Couldn't prove murder, just like they couldn't prove the kidnapping charge. However, if they lose the case of kidnapping then they could still go after her for murder if the body was ever located. If the body was never found then they could arrest her for murder and let the roll of the dice hope for a positive verdict.
Interestingly they have only gotten the husband on a charge of obstruction of justice. His case for the kidnapping charge resulted in a hung jury.