How to tackle a hard situation and not come off like you don't care.?

My wife of 6 years, found out in Febuary that one of her close friends from when she was growing up died 7 years ago. they had a memorial, but even now months after, she keeps a picture of him on her dash board in her car and for some reason cant move past it and it is starting to drive me crazy i have lost several friends and family because of my job (military) and i can not seem to understand why she keeps holding on. I understand everyone mourns different and for different amounts of time but now they are trying to do something for his birthday,so i just dont understand.,I am not a cold or calus person by any means but i am hoping someone can help me understand thanks !!!