gavra and Sam: The OP wrote “potential boss”, so apparently she was not yet hired. And if she was, we go back to my original point of him being forced to choose between breaking halacha (since he can’t see her hair) or breaking secular law.
I didn’t see that. I agree with you, but just point out that he will possibly have a losing discrimination lawsuit (just like if he would not hire a non-jew for the same reason). He should ask his own LOR what to do in this case.