These are actually two different skill sets and there is no reason why working on the less developed skill set has to retard the better developed one. I also think that using a graphic organizer typed approach will help her develop more coherent writing. By 4th grade, that approach should be fairly familiar as our schools begin teaching it by 2nd grade. Perhaps you can reinforce it at home?
It's great that her teacher is not penalizing her for producing a product that may depart from the guidelines. Fortunately, by middle school, multi-media projects are fairly common although students are still required to write well-supported paragraphs in "black and white" as well as within the multi-media products.
I have not had your exact issue with my kids, but I have noticed something somewhat related with my twins since they often have the same writing assignments. My artistic DD tends to favor form over substance in her writing while DS is the opposite. Both form and substance are important and I end up praising DD's form and reminding her to bolster the substantive content and praising DS' substantive content but telling him to improve his form.
