By the end of the book it is made very apparent that Oskar's mom loves him very much and has been very concerned about his coping with the death of his dad in the Twin Towers during the 9.11 attacks. We find out at the end that she has actually been orchestrating his "adventure" to finding the lock that fit the key found in his dad's closet. The novel opens with the family attending funeral for the father, even though they have no body to bury. I am sure the mom would talk about the shock of her loss, how scared she is to be responsible for raising such a bright young boy on her own, how unjust the attacks were, and how odd it is to be burying an empty casket. She would probably explain how doing this seemingly pointless act is actually something she needs to do for closure.
Once Oskar starts on his quest for the key, she would probably talk about how she encourages the activity as a way for Oskar to deal with his loss and as way for Oskar to still feel connected to his dad. She knows that Oskar takes things very seriously and is wise beyond his years, and she uses this quest to help him heal. She might reveal earlier in the novel that she has arranged for Oskar's meeting of the characters named Black and that she hoped that Oskar would be able to learn something about the human experience from what each of the these people has had to deal with in his or her own life.
She would likely include some comments about how she has been able to move on in her personal life with a man named Ron. He too has lost his wife, so they share that experience. Being with him doesn't diminish what she felt for her husband, but it is proof that life goes on after the death of a loved one. She might express concern over how Oskar feels about Ron as he is not accepting him easily.