Circular reasoning only proves that the question asked has gone unanswered... claims of fait accompli notwithstanding. And the suddenness appears to be your creation alone, as I can find no other online reference to mental illness or insanity attributable to Ms. Maire. And certainly none related to the quantity of photographs she made. Or never got around to developing.
Do you have privileged access to medical data of which everyone else is unaware? Or are not privileged to disclose publicly? Otherwise, just exactly how did you come to your determination, given that the poor woman has been dead now for four-plus years? Perhaps you knew her?
N.B. At best what you are proposing would seem to be a raw hypothesis, not a theory. In general scientific usage, a theory would be "a well-confirmed type of explanation of nature, made in a way consistent with scientific method, and fulfilling the criteria required by modern science."* Based on what you have related here thus far, I don't believe you're quite there yet. Especially with that pesky "well-confirmed" part...