Here's how to make it work for NuTrek:
By the time Kirk and Spock arrive in 1930 Earth, make it where Bones has already been there for about three months and has been doing house calls for the unfortunate in the soup kitchen. Make McCoy
the one who falls in love with Edith. (Kirk's got Carol now, and Bones is younger and still struggling to recover from a far-more-recent divorce.) When Spock's semi-repaired tricorder reveals the alternate-future Edith to be Edith McCoy
, that's where Kirk faces his big dilemma - to save history, he not only has to let an innocent and kind woman die, but break Bones' heart all over again... and risk losing him as a friend and officer permanently.