Graveyard scene

I've watched this movie many times and just noticed that the woman at the graveyard scene is Mrs. McCabe (the woman Tadgh gives the book to after Bull goes aside).
When Bird and Tadgh talk you see Bull doff his hat to her in the background.
Did anyone else think this unusual given their relationship or would husband and wife have done this at the time?
She appears to be coming back from Sheamie's grave where Bull is going; maybe it it this shared respect for the dead son.