I agree entirely.
My company has very different standards for when we're working internally than when we're working with customers. If we're working internally, shorts and flippies are fine. If you're on site, show respect for whatever the local culture of the client is - if that's business casual (it usually is), do that. If it's a damned suit, wear a damned suit. It's just not that hard.
In the case of the OP, it seems obvious that this person is difficult by nature and the company would do well to replace her regardless of any attire issues.
The people always going against rules on the workplace or coming there dressed like a slob never go anywhere in life.
Why is it so difficult to dress proper for some? Money can't be it, you can dress in a decent shirt, pants and leather shoes for the same price you sometimes pay for just a pair of sneakers.
I say that because, if they are bad enough not to have foreseen this (in case it was indeed a mistake to not have a dressing code), then they will probably be bad again and make a dressing code much stricter than what they would have accepted before all this mess.
you don't really work in corporate America do you? this kind of thing is pretty standard. But instead of describing it like you did, the boss would be more like "This is our professional team working diligently to serve your needs". The idea is to minimize the visit and make as little stand out as possible.
The headscarf is stupid looking, but it's whatever.
What I'm referring to is the part where someone says, "oh, you want me to wear something different, well I'm to cosplay and sue you". Maybe she'll win the suit, but not having this person working for you would clearly be the best outcome for the company - this is a really dedicated troublemaker.
Why do you think this? I am generally curious, 99% of "professional jobs" have you at least wear collard shirts with slacks (if you're a guy). Personally, if i go somewhere were i expect a professional environment, i expect people to be dressed fairly professional, i would want to take a mortgage out from someone in gym shorts and a white t-shirt...