How to motivate an already smart child to care enough to do schoolwork correctly?

She is in 3rd grade doesn’t struggle to understand concepts at all but she doesn’t care if she writes it down right or at all.    Her grades hurt and when I review things with her she can demonstrate she understands so it’s frustrating.   She will solve the homework question without hesitation then writes the wrong thing down and is annoyed when I tell her to fix it...