Yes! I can't believe I forgot the DWJ. Also Tanaqui in Spellcoats, who is weaving her story into a robe, which is in turn translated into the-book-we-are-reading. The book actually ends with her in the act of weaving in her desired ending and saying "WELL I HOPE THIS WORKS."

Also also Mig in Black Maria, which -- I can't remember if she actually explicitly affects anything with her storytelling now, but here again the book we are reading is her story as she is telling it, and there is tons about gender and the power everyone is fighting over is the power of creativity, so there's got to be something in there.