I’ve been at chassanahs where the kallah keeps her hair covered at the conclusion of the chuppah and comes out of the cheder yichud with her shaitel on. It is a little bit of a balagan trying to get things straightened out, but no worse than the chassidishe kallahs who come out of the cheder yichud with the chassanah tichels on.
As far as the whole issue of make up goes, I see more and more kallahs with a thick coating applied, almost masking their natural beauty plus the glow they would surely have on this most important day of their life. The hanhala of the school may be seeking to give them an example that hits close to home for the younger girls so that they can see how their friends look beautiful even without the extra coating on their faces (which by the way cost a pretty penny to have done professionally). And since all the makeup gets rubbed off during the course of the chassanah so there is little for the chassan to enjoy anyway. And since a lot of the family pictures are taken after the guests have all gone home and it is just the family and close friends left, who is to say that she can’t put on some makeup to make those pictures come out nice, especially since she’s all worn out from the excitement and dancing and all.