So far all that you have written about her is what she looks. This is just one small part of character design. What you need to is make her breath, and let her life inspire your design.
Ask yourself questions like: What is her greatest fear? What does she want to archieve in life? Does she know of herself what she wants to archieve? Is she loved? Does she like that?
When you ask questions like this you get to know her, and when you know her you can start asking about what kind of clothes would she wear? What kind of cultural symbols does she use on her clothes? Is there a dresscode in her world, and is she fighting that?
Good design comes from knowing your character and imagining them in stories. The actual designing and drawing will become easy, because you would be drawing something that already excists.
edit:
Just a quicky. For example I imagined her to have lost her father, and desperatly want to get into his footsteps, even though she isnt ready for it. Her insecurity led to her wearing her fathers clothing, hoping to come off as big and intimidating as he did.
While thinking about this you can't help yourself from drawing this young girl running around in a way too big overcoat