Re: Final scene of picture--who was behind the counter?

You're right, that IS Maggie's mother working behind the counter in the diner. In an interview, filmmakers said the movie "turns on the final scene of the film", where everything has been, in its way, corrected. Eddie has his final fight (with Willie), and Maggie first attains her dream of boxing, and in the end, receives the peace she wants (from Frankie). Frankie gains a daughter in Maggie (in effect "replacing" the one Eddie has been writing to), and has bought the diner (its connection to Maggie gives him peace). Furthermore, Maggie's mother is behind the counter - her lack of employment and unwillingness to work has been a point of contention throughout the film (contributing to her lack of gratitude when Maggie buys her a house, because it puts her welfare status at risk). By employing Maggie's mother and thereby making her responsible for herself, Frankie has mended Maggie's family (something Maggie would've wanted), and it gives him the peace he cannot find with his own estranged family.