We do extra work in writing with my middle school ds, but we're coming from the opposite end of the spectrum - he's 2e with an expressive language and written expression disorder, but fwiw, maybe some of what we do might help.
The first thing is, I do review his work and help him out with suggestions - if your child is ok with this, I'd keep doing it!
Second thing - do you think it would help your dd to hear her writing read back to her? That helps struggling writers, but I'm thinking it might help a good writer too - you could either have her read it back to herself, you could read it to her, or she could use a text-to-speech option on the computer if she's composing on the computer.
Reading - I honestly think even as students get far along in school and develop their writing at high levels, reading that supports what they are learning in their writing helps. If your dd likes working with you, you could help by picking examples of specific types of writing to read and discuss together.
Journaling - fwiw, we don't do this with our writing-challenged ds, he's too challenged! But I do this with my dds, both of whom love to write. They're younger, but I think it would work with older kids too. It's a simple journal where we write back and forth to each other. I started it with a dual-goal - sharing our thoughts, plus working on writing conventions. We read what we write together, and I make suggestions on how to improve the writing.
I hope some of that helps!
polarbear
