I agree with the general sentiment about putting away the special dolls. Casper is too young to be able to appreciate the value, and if she does damage one (which will be a strong temptation because, forbidden!) she will not understand the depth of your upset. Later, you can bring them back out. The only thing I'm hesitant about is because you set a parameter (if she damaged them, they'd disappear) but would be preempting that condition and consequence.

I was the sort of child who got upset at irrevocable damage done to toys. So yes, I still have a couple of my infant toys that are in fine condition.

Anyway, I was wondering if it wasn't something specific about the act of haircutting. When I was a kid they had those weird doll heads that you could pull the hair out and cut it. Do they still have stuff like that? That way, Casper could have a specific doll that it was okay to cut, and maybe get out her creativity harmlessly?