Quilter's Dream Cotton Request is the thinnest, flattest batting that I know of. I, also, really like all the Quilter's Dream products.

If she lives in CA maybe she does not need a warm quilt. I am making one for my granddaughter and I am going to use wide muslin to replace the batting. I am going to have it meandered so that it does become stiff with the quilting.

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!!

use a piece of flannel

I use white fleece.

You can use a sheet for batting. Some of the "old time" summer quilts used them.

Thermore is the flattest that I've found.

I would go with a thin poly batt. You don't have to 'overquilt' and it stays thin, hugs the body, but has no real weight.

I use Warm and Natural, Warm and White, and Warm Blend - all of which are nice and flat. My quilting is not close together but rather stitch in the ditch for the most part. After a few washes, the quilts are flat and they conform to the body. My first quilt (made in the early 90s) is silky-soft by now. Love it!

Thank you to all those who replied...I am thinking we will go with the Quilter's dream request...cotton of course. But still not sure. Still will be a while before I finish the top. It is interrupted to make a baby quilt. Plus I am waiting on fabrics to get here.