Last Person Hannah Sees: Librarian Poet

As Hannah is going into the post office to mail the box of tapes, she runs into the nice librarian guy from the poetry group. They exchange pleasantries. She smiles and acts completely normal. There is no indication she's about to kill herself. I wonder what others took from this and why this was included? He was a very minor character and it seems like this is a completely unnecessary thing to include.
So is there a message we can take from this?
I'm thinking that it reveals one last last chance for her to open up to someone about her issues, and she still lets nothing on about what she's going through. She doesn't give any clues that she's in torment to this guy who is all about self-expression and being open and honest in poetry. To me, this shows that she ultimately is responsible for taking her life because she simply didn't or couldn't open up about her issues and ask for help. She was effectively already dead at that moment. I don't know. I just found it a very sad scene.