>>211870795Not everything has to have a relevance to the plot. It's just a compelling scene that helps Margie appreciate what she has.
Some people say the point is that Margie after discovering Mike was lying suspects that Jerry may have also been lying but this is wrong, there's a scene written that was cut where another cop tells Margie about how Shep is wanted for arrest for assaulting his neighbour and a possible accomplice connected with the murder so Margie goes back to see if Jerry's been in contact with Shep.
I guess by omitting that scene you could say they were alluding that discovering she was deceived made her go back to double check her tracks but it wasn't originally written that way.