Oh thank you! I think a lot of it comes down to faking detail, but I after like 25 minutes I reached a point where it was just diminishing returns but it still didn’t really look right... Anyways, for the hair in particular I just copied what I saw art gods like Craig Mullins, Guweiz, and WLOP do in their art. They break the hair up into larger shapes and then "fake" the detail with a few thin brushstrokes and possibly some texture here and there (this is a general rule for digital painting in general, but it's especially important in hair). Here's a good example of this (if you haven't seen it already):
I'm not super good at this kind of stuff yet so I'm not really sure whether I have the authority to even talk about the processes I use for digital painting but yeah, hopefully this helps! 
