A father who is unaware of the mother’s MBP and who supports his wife could very well be an unwitting participant in this particular kind of abuse.
Also, I saw some mention of an older sister who supposedly has a mitochondrial disorder—so there is some evidence that another child has been affected.
I would also expect that as the mother’s psychiatric disorder progresses, its manifestation would become more severe and sophisticated. Thus, the older child might have received a diagnosis of mitochondrial disorder after many visits to many doctors, and the mother would have used that experience to refine her technique on the younger child.
Please note that I am only saying that Munchausen’s is a distinct possibility here, not that it is a definitive explanation of what is going on. We do not have the full facts here and have no clear basis on which to determine what is really going on.
In most Munchausens by proxy cases by and large, when the parent is closely watched, the parent is found to be deliberately poisoning or doing things physically that cause the child to be sick. A mitochondrial disease can be shown via lab tests. If the child is shown to be physically worsening under the state’s care, it may be that the state is actually in error.