This was a really powerful article by a therapist who lost his young son (and works a lot with grieving patients):

http://opinionator.blogs.nytimes.com/2015/01/10/getting-grief-right/

The last sentence here was especially powerful:

<< I suggested to Mary that there was nothing wrong with her. She was not depressed or stuck or wrong. She was just very sad, consumed by sorrow, but not because she was grieving incorrectly. The depth of her sadness was simply a measure of the love she had for her daughter. >>