Long story. But the short and the long of it is....
My MIL has 2 sons and a daughter. I married the middle boy 
Each of them has a daughter - so MIL is a granny of three girls (two years or less apart in age).
Historically, MIL not keen on me but appears to like my posh SIL.
Today was one of my nieces birthday parties (MIL's daughter/ hubbys sisters child). It was a big family doo.
My other SIL was there with her daughter.
I was there with mine.
Both my nieces had on matching, expensive looking party dresses. One was the birthday girl of course and the other was her cousin too. I head my SIL say to some distant relation that MIL had bought them matching dresses.
AIBU to think it is a bit weird to buy two out of three of your grand daughters matching dresses and not the third? It was a family only party and they were the only three little girls there. All cousins.
My daughter spotted their matching dresses. I distracted her and did not look as if I noticed whatsoever. But inside I did and I think it was a bit wide of MIL.
AIBU?