On one occasion, when my sister and future husband visited to see eldest son, baby's mother and baby, the baby's mother "hid out" at a neighbor's house, while my sister was visiting, leaving eldest son to lie about her being at work. It was later revealed that baby's mother did not wish to spend any time in the same place as my sister.
So, from the DIL's perspective she could have been giving the OP's sister time to visit with her son and granddaughter alone. I don't see anything wrong with this and think the son culd have worded it better. "Oh, she wanted us to have sometime alone." or something that did not need to be "reveald" hurthurfully lately. Heck, I live with my mother and I sometimes leave to give her time to be alone with someone who's in from out of town.
One of my brothers married a truly toxic person and we still tried to make her feel welcome for the sake of my brother. I simply can not understand the idea that all the blame in this falls on the GF.
I'd like to hear the GF's side of all of this. She treated the actual mother rudely in favor of the ex step mom? Or could she have just been more comfortable with the person she knows better, and not sure of her self around the OP's sister and not sure how to act towards her? The baby's grandparents were there, but not the rest of the famil? perhaps in the GF's family of orgin extended family is not invited to such things.
The toy thing would bother me, but do the parents of the childhave rules about toys that grandma is not following?
There is something more going on here....the indications that the GF is snippy over facebook comments from and Aunt in law she's never met, and that there was once a good relation with the GF and the OP's sister tell me that.
Honestly I think the only innocent in this is the baby - the one who is going to loose out on knowing ALL of her family. As someone who grew up rarely seeing her father's family. I would urge the OP sister's to reach out to the future DIL and try and repair the relationship
-- and be open to hearing the concerns from her son's family.
There is no evidence OP's sister has ever done anything to make then feel unsafe to have their child around her..they want to use an innocent child as a bargaining chip.
We are only hearing one side of the issue and the OP's sister is not coming off too well, to a good many people - I maintain that there is more to this story.