You could test the idea by showing her a few photos - different themes on different days - and seeing how she reacts...
I see what you're saying about it being cruel to remind her of her past, but I'm thinking more and more now that my mother actually needs to retreat into her past as an escape from the present, which she doesn't like.
For example, she cannot walk independently now, but she regularly tells me how she went walking back to her old house (that she lived in when she was 30, or 20...) and visited it... I feel she needs that.
When my husband could react to his memory book he was certainly more animated about the older photos of our early life together than he was about the more up to date ones. Many of the photos contained friends and family who had died and he talked about them as if they were still with us.
I can remember him saying one day when looking at a group photo of our wedding, that his Mum looked nice in her suit and she should wear it more often. His Mum died nearly 30 years ago. We seemed to have more confusion with the recent ones where he had forgotten the person but it was not upsetting just a comment along the lines of ' Who is that'.