a better ending (spoilers)
Maybe I'm a pollyanna who wants to have everything work out okay in the end, but I think the movie should have ended with Susan Sarandon's line "I'm her mother." I think throwing the bit at the end where we find out Blunt is not her daughter but a friend at the orphanage is just a twist too far. Or if they wanted to do that, they could have had that plot development take place earlier in the movie so there could have been some sort of final confrontation between Sarandon and Blunt.
But personally, I think ending it with Blunt and Sarandon just embracing would have been...nice.