Alice here:

This old woman can be mythic.  In fact, since we've read Portrait and Ulysses in class, I've learned to watch for old women.  In Portrait, for example, when Stephen is overcome with sin and can't  find the church to confess in, he meets an old woman who tells him the church is on Church Street--he was so messed up he couldn't think straight to figure that out for himself.    It's a crucial time for him, a crossroads in his life--as it is in Ulysses when the old milk woman arrives.

And here, if we realize what's going to happen to the boy, what he's going to see--even if he doesn't quite understand it just a few pages later when the story abruptly stops--we have to realize that if  this old woman didn't beckon him into the room with her bony fate-like hand, he'd would never learn.  So, she's a mythic force even while she's just the priest's broken-down cliche-ridden sister. 

You may have realized that we have three women in that room.  The Three Fates?  Why not?  What do the Three Fates do but direct human destiny?  Oh, here I know one "sipped" instead of "snipped," but was not Father Flynn's fate  (to become a priest) directed by forces embodied in those women?  Think about that!