Did you read this?
https://www.amazon.com/Mary-Todd-Lincoln...0880640731
My copy is far away, I cannot check her letters after Batavia, but I think not everyone though her "mad".
Especially her grand-nephew Lewis didn't.
I, too, think Tad's death was just too much (her husband's had been already), and if anything Batavia brought her back to reason because getting out needed this (Batavia worked like cold water in the face. Despite I think it wasn't good for anything - well, getting to know her son's mindset).
Didn't her sister Elizabeth, Robert's aunt, have one mentality ill daughter? Was she institutionalized? No. IMO Robert just wanted to get rid of a problem the most convenient way for him.
Madness of Mary Lincoln
