Again, this is something that was written after Lincoln died. There’s no way to “prove” the veracity of the statement, though two people, IIRC, gave similar versions of it. Some authors accept it, while others scoff, and say that it’s just part of the Lincoln-as-Visionary-Martyr legend making.
I believe it was several years, if not more. I’ll have to check my biography of Mary.
Mary was never very frugal, which is actually one of the manifestations of her so-called insanity that her son, Robert, used to get her thrown in the asylum. (“She buys things she doesn’t even * need. *”) At times, she found herself in need of funds, and some say she hoped to play off of the Bereaved Widow of the Great Man image by getting people interested in her side of the story, and maybe make a little money off of it. Nevertheless, her versions varied, just a bit, each time she told them.
Maybe her grief did make her a little loopy. She certainly was a sucker for any charlatan that could “contact” her dead huband, and she had that famous spirit photography session.