Reddit users slammed the woman's words to her daughter and explained why they thought she should include her daughter's foster child in the photo.
"What's the worst case if the child does move on to another home?" one user replied.
"Having to explain to your dear cousin Cletus that, 'Oh, that was the baby girl who my daughter quite generously brought in, took care of, and treated as her own; I loved her very much and I'm so glad I raised a daughter so caring, and I really miss the girl. At least she's found a permanent, happy home'."
Another person asked her to put herself in the adoptive child's shoes seeing the photo and wondering why she wasn't in it.
"'Why am I not in these photos?' She asks her dear grandmother," the person wrote.
"You were a foster child and so I didn't consider you my real grandchild, lol, so I refused to have you in the picture. Sucks, kid."
The grandmother responded to the comments and tried to explain the situation further.
"I do care about this child, I'm not trying to exclude her purposely or out of spite. I just feel weird including her in our photo when legally she is someone else's child still," she wrote.
Reddit users remained unconvinced.
"Let me give you a hypothetical. Say she adopts that child, that kid who potentially will forever have abandonment issues looming over her head," one person wrote.
"Now imagine she learns that her grandmother didn't want to include her in a family photo because according to her she isn't a part of the family because 'she might just be temporary'."
In the end, the grandmother admitted her initial reaction was wrong.
"I accept judgment…I feel the need to say that a large majority of my concern is precisely from a legal standpoint. I did not feel comfortable claiming this child as ours when, although her parents are being irresponsible. Maybe I should have expanded on that in my original post; if so, I apologise," she said.
"I am not a heartless monster who rejects anybody who is not blood - I'm an old lady who is confused on the customs and socially acceptable behaviour of a new thing (foster system) in our lives and didn't know how to act or react. Thanks to everyone who kindly explained to me why I was in the wrong."