Well, for one, her face looks very long, when in reality her face is lot broader. I think getting the facial structure right before adding shadow would work well.
I get the feeling you draw purely what you see, without fully understanding how the face works and why you see what you see. I can be wrong here of course, this is just my first impression.
In the last few months I myself have been trying to learn the Loomis method of setting up a portrait, and I must say that really helped me. See, at first it seems overly technical, but once it becomes second nature it's an easy way of making sure the proportions are realistic, because once you know how to quickly set up a proper basis, you can't really go all that wrong with the details, because the parts of the face are already where they should be.
Stan Prokopenko explains it well:
Now, I can't guarantee you'll find it a pleasant technique to work with of course, as everyone has their own workflow, but I think it's worth a shot. Another thing I'd recommend is; draw a ****-ton of heads. Like, not a portrait every now and again, but fill a whole bunch of pages with them. All sorts of people, too. Young, old, fat, skinny... Try to find pictures that aren't retouched in Photoshop all that much so that you can observe the face in as natural a state as possible.
I personally often use mugshots. Not very orthodox, but mugshots are the most raw you'll ever see most people. The light is unflattering, the emotion is real and there's not effort put in to make it look pretty. And that's why I think they're good reference material.
Humanae is a blog that aims to photograph every human skincolor there is and the artist behind is does not photoshop much, so that is also a very good resource.
But the bottom line is just really; keep drawing. You don't have to work out every one to the same extend. If it doesn't work out; whatever, try again.
Another thing I'd recommend is studying the facial anatomy. What influence does the shape of the skull have on the shape of the head? Which muscles are responsible for what? Where do you find the most fat tissue? etc. Really trying to understand how everything works has really helped me improve my portraits, wether they were drawn from a photo or from memory. Once you are very familiar with how the human anatomy works reference becomes a loose guideline instead of something to follow super closely.
Here's some reference that might be helpful that I've found all over the internet:
Hope this helps.