Best way to isolate a head garment from a face

Hi, I'm really new to Fusion and to VFX in general, I have something very simple (I think) to accomplish but I'd like to learn how to do it the best and simplest way. In the shot, the actress is in darkness and wearing a black scarf over her head. She moves a bit and the folds of the scarf with it. I need to isolate the scarf from the face so that I can work on that part specifically. I'm sure there's many ways to do it, but what would be the best tool to do it in the simplest and most accurate way possible? There's a good contrast between the scarf and the skin, which is light.
Thank you:)

The simplest and most accurate way to handle it is with the poly tool. Draw an outline around the scarf and use that to do what you need to do. Even if you're able to use a Luma key or something to get some of the scarf, your going to need some type of mask to take care of random extra things. Google how to rotoscope in Fusion and go from there. It will help you know what can be done and the proper way to start the process.

What do you want to do with it, when you say 'work on it' ? Do you want to isolate the face as if everything is black?

Thanks for the insight! It's for some patching up, basically I want to copy part of the scarf on one side of the face and mirror it and apply it on a small part of the other side of the face that needs to be hidden. As I said the scarf is fully black and so is the background so I think it could pass.