That's an excellent illustration of the principle, Gk.
Bags It's not a question of smartness per se, as about individual identity vs corporate identity.
It should be made clear it was not PwC who imposed this rule, but the agency which sent Nicola there.
But when you choose to work for an organisation, whether it a multinational corporation, a hospital or a school, you take on board tyhat organisation's ethos, guidelines and regulations. If that includes a dress code, so be it. Of course if there are health reasons why someone can't or shouldn't wear 2 inch heels, then an exception should be made, but that is already covered by existing legislation.
And yes, any job which involves interacting with the public involves and requires acting.
You go to work feeling depressed, anxious, miserable or angry and you have to hide that and put your happy face on, because the public, your clients, customers, patients or pupils, and your colleagues, are more important than you are. That's acting.
I think too that laws should be made from principles and not from individual grievances.
Finally, a disclosure. I wouldn't allow my employees to wear sandals or open toed shoes at work because I thought they looked wrong in a clinical environment.