Whether it's a thing or not, I'm not aware of any rule against Ivanka Trump taking on the First Lady role. But for me, the question is, what was she thinking to choose such a 'look at me' coat for that particular occasion?
She was there to honour a dead serviceman. If you're the bereaved family then you wear whatever gets you through but otherwise the first rule of dressing for such a sombre event is surely to not draw attention to yourself? I'm not saying you shouldn't wear anything expensive or designer but if ever there was a time for an understated piece of Ralph Lauren, it was then.
Very poor judgement - and I thought Ivanka was supposed to be the smart one of the family?