Every photographer needs to make their own call on this based on how well they know their client. My opinion: I think you want to decide this with your client.
If there is a temporary red mark on a clients face and you take it off, or reduce dark shadows under they eyes, take dust or loose threads off do clothing, a client is unlikely to mind or even notice. If you fail to take such things off, they are likely to notice them .
When it comes to features which are a part of them, removing them without asking can backfire. Badly. Because you are making a judgement about there being something wrong with who they are. She, her family or her partner might love that "feature" which is not a flaw to them.
Making credible moves which reduce the emphasis on a feature is generally safe. So, if the hair stands out because it is darker and you make the color be closer to the color of her skin without removing it, you are making what is probably good move. If the hair is creating shadows or has highlights on it and you reduce or eliminate the shadows or highlights, again this is good. If the light is emphasizing the issue and you reverse the effect or if there is a way to light her that deemphasizes the issue and you edit so as to give the impression that is how that part is lit, that is also safe as long as it is credible. Same goes for protecting this region from contrast enhancing or sharpening effects.
Models will probably expect to be Photoshopped, but even so, there are lines better not crossed. I remember a rant about a photographer who removed a tattoo without talking with the model first .