You might want to ask her why she decided on batting after all. If it's because she wants to see the quilting ... that will give you a better idea of what kind of batting to use. As FelineFanatic said, you won't see the quilting definition in most of the flat battings.
If she wants it for a bit more warmth, consider using a wool batting which is NOT 'flat' but it is light weight (compared to W&N), and is actually warmer than W&N in the winter and cooler than W&N in the summer because it breaths more (and is not as dense). I just put a wool quilt on my bed and the temperature is just perfect. In the colder months I add another blanket but thats just because I live in Chicago and sleep with a window open all year!!