I don't think it's that big a deal that she did that, because she was trying to rationalize her irrational behavior. That's perfectly normal, not nice or all that clever, but normal. I am sure she is on a mothering board somewhere, or among her friends thinking "My SIL, while I was in the middle of trying to get my kid to eat her dinner, went and got her son DESSERT, before he had finished his!!! Isn't that NUTS!?" so I can see why she was trying to explain the situation to her DD. Assuming her DD has half a brain, she cottoned on quickly that mama was telling tales.
Â
I have a SIL who has very different parenting style from me,too. I try to explain to DS, who is curious about the sort of yelling that goes on, and more specifically the threats of spanking and eventual carting off to be spanked, and/or locked in a room against their will...He understands now that we just don't do that, and it is sad for his cousins, because that is their parents' choice, but we can teach them how to communicate more peacefully.
Â
We choose to spend less time with them as a result, because frankly I don't want my kids exposed to unneccesary violence, especially when at a place they should consider homey. When they come over to visit us, I house their kids and get the grown ups a hotel room so we can parent the way we like in our home, without the threat of violence looming over us. They just don't have any interest in finding out why kids do what they do, or why they say what they say. They just have ZERO curiosity about it. They consider it their job to raise non-criminal, non-waster, socially-normative kids into socially normative grown ups...That's it. If they happen to come out special or do something amazing, awesomesauce...but that's not part of their job description  to foster whatever hints of talent or uniqueness might be lurking beneath. So, yeah...as a teacher, I obviously disagree there.They just desperately want to find a way to force their kids to toe the line, and especially since the first two were so mild mannered, they are struggling with the third, who is close in age to my DS and the more you push her, the more defiant she gets. DS frequently gets compared to her, and not surprisingly, later on he frequently gets bitten or scratched by her in an attempt to express her anger over being compared to him unfairly.
Â
Here's what I would say next time BEFORE going to get the alternative food: "Hey, SIL, can I see you in the kitchen for a sec?" then "So I think I might have given the kids too much of that. I'm going to take away DS's and wrap it up for a snack for tomorrow. Do you think if I made them something else, like plain yogurt with fruit and granola, they might eat that?"
Â
That way she is a part of the plan, and a part of what's happening with her DD. Then she might have the chance to say "Can you please wait five more minutes? I really want to take a stand on this issue." (for whatever reason) or "hmmmm, Maybe you're right...okay." or "Can you call DS into the kitchen to have his yogurt? I still want my DD to eat her broccoli."
Â
I would probably be annoyed if my SIL let her DD3 go ahead and do something that DS was not allowed to do before meeting criteria XYZ. The difference is I would not lie to my son to rationalize it, I would tell him the truth, (even at not quite 2), because he is smart enough to look at his cousin and say "ummmm no, she didn't!" And that would open up a whole host of issues between us that I have no interest in exploring...like: "If Mommy can pick and choose when to tell the truth, why can't I?" Or "how do know when I can trust her and when I can't?" KWIM?
Â
As an aside, can I just say...at not yet 2, I think your SIL is being really silly...mealtimes are pretty much serious goofiness with only 10% nutrition at that age ESPECIALLY if there are other kids to goof off of. OMG. I usually could get DS to sit for about ten minutes at dinner at that age. I usually just left a tray of various bits and pieces on the coffee table for him and let him graze and play while we adults enjoyed a peacefull meal together. Of course that means that it took him until he was about 5 to learn how to sit and eat a meal with everyone, but a typical grown up meal lasts about 1 hour and that's a long time for a little person to stay seated...physically, that's tiring for them, and that's definitely going to have a knock on effect in terms of eating something they don't want to eat. Of course if your SIL is like mine she will not give a hoot, because darnnit all, they need to learn the rules.