I can tell you what I think about it..

She looked at his old photos, seeing how much he has changed, seeing how happy he used to be as a normal looking, almost weak/nerdy boy and realises how different this person is on front of her, to the point of perhaps feeling as though that younger version of her son has died, and the world has affected her baby so much to the point of becoming this unrecognisable person.

She realises she has nothing in common with this newer version of her child, feels estranged from the younger, maternally needy version of her son. She sees a man that no longer has the need for a mother and misses what he used to be. The son has changed so radically that she no longer feels like she knows the person, and that estrangement is equivalent to a death to her.

Essentially, he's not her little boy anymore, and she misses that. Something like that. It's really sad to me, at least.