The dress is very FROZEN ELSA, as others said.
Let's have a look on her Ice Blue "I AM ELSA" collection:
This collection does not include the ice blue mullet dress (which was like knee length shift dress with a long curtain draped over and would have been inappropriate here)
and the ice blue number dreadful McQueen taffeta number she sported recently for the NL state visit, which she possibly could not repeat so shortly after.
Of all 4 above, yesterday's is the most girliest one. I would have preferred the second from left (one of my all-time favourites), which she originally wore to a movie premiere. If this wasn't shiny enough - heck, she could have had some sequins added ... it would have looked much more mature.
The other two, I hope, have already been banned (the second from left is maybe still too tight, but as she still seems to be on the weight lose trip, there's a chance; the one on the right is a tad too dark to look good with her hair color, and has for sure too many sequins to be ever worn together with a tiara - plus: it would hang on her like a potato sack, as she had like 10 kilos more back then).
If "light color / monochrome" is really the dresscode, she should go for a light lilac - suits her color palette (eyes, hair, skin) much better than the ice blue.
Remember this one?
Simple and chic. 7 years old. But she would still fit in.
And yes, she should work on her posture. The bobblehead seems to drag her over, and the tiara in combination with the hairdo just adds to this impression.