I first ran Surface Blur with a Radius of 1 and a Threshold of 5 to reduce some of the graininess on her face. Then I applied Local Contrast Enhancement as shown in the pic below:
The result is this:
Then I ran G'MIC (Boost-Fade filter with settings as shown below):
Which resulted in this:
(There's still a good amount of graininess on her face, so these are intended merely as possible starting points for further improvement)
Alternatively, I also tried applying the Boost-Fade filter alone, with no previous effect, but I think the outcome turned out rather colorless, although her face seems to look a bit less grainy than with the previous method:
So, in order to enhance colors, I applied the Laplacian Pyramid Filter with an Outlier reduction of 50 and an Extra contrast of 0.55 (all other settings at defaults), rendering the following result:
I tried other methods as well, but didn't like the outcomes very much. I hope my take on the matter may help somehow (I feel I prefer the second method but that's up to each eye's taste).