Why in the heck did she do this? I didn't see any reason given in the article.
Did they test for the other ingredients in what she gave him? The argument being, if the other ingredients weren't also in the stomach, why would they expect the salt to be there? If this concoction she gave him wasn't the reason for the high salt content in his blood, what was?
Low sodium content in the stomach doesn't sound like a good enough reason to release her unless some of the above questions are answered somewhere else.
She was accused of poisoning her son. Tests show absence of poison in her son's stomach. What else has anything to do with the case? What does it matter, what was she thinking, if in fact she is not responsible for the child's death? You are almost going after some sort of thought crime.
If there were toxic levels in her stomach, then and only then one might ask what she was thinking that led her to feed him a toxic dose, and does it rise to murder or whatever. But not in this case.