Drawing detail in dark hair?
As fixer1234 mentioned, in your photo reference, all the hair falls in the darkest area of the spectrum of light values. It actually won't matter once your drawing is complete: once all the light values are on a similar scale, just filling the silhouette of the hair with the darkest value you've used elsewhere in your drawing will create an effect similar to that in the photograph - the flat character won't stand out anymore since we humans are accustomed to images having a limited value range. A famous (and quite rare) art historical example of this, is Vermeer's Girl with a Pearl Earring:



See how the nose bridge just disappears into the cheek? Yet, it's not conspicuous at all (this is actually one of the reasons the artist David Hockney convincingly reasoned Vermeer used a camera obscura to paint most of his works. But that's a different story altogether :).

If you do want to draw it, you first have to understand the structure of the hair. For this, you can easily find reference material online. Here is an image that shows at least a little of how her braids are structured:



Hatching is a viable option, if you follow the direction of the hair as it curves around the volume of the braids. As the light source in your image is on the right, you can add slightly lighter patches on the right sides of the 'lobes', by hatching with less pressure, by leaving small gaps as you hatch so the paper shines through, or by using an (kneadable) eraser.