Your friend was wrong to comment. I can't think of a nice way to complain that someone didn't post photos of you on FB.
And in the same vein as Facebook, I looked for a way to "Like" your post! You are so right.
Lordy, do I have to check each photo before I post it to make sure everyone present is accounted for?
I think it's the fact of the sheer quantity of pictures and the MIL was not in a single one. While it could be just careless, it would certainly make me wonder, especially if there was a history with the MIL and DIL.
Perhaps she could have commented something like "Great pictures! Could you post that one of me with John and Mary? I really wanted to see how it turned out. And maybe the one of me with you and Son? Thanks so much! Love the collage!"
Then she's specifically asking for the pictures and if you read between the lines, one could figure out that she realized full well that there were none of her. But she's not calling out the DIL specifically, and it doesn't sound like there are hard feelings (at least to me). Just....hey, can I see the pics with me?
Alternately, if the relationship
is good enough, the friend should ask her own son what's up and tell him that she'd like to see some of the pictures that were taken of her.