I would use ALL the fabric, no matter what it is, corduary, wool, jeans whatever....it is more a memory quilt than anything.....What is your mothers most favorite color, purchase a nice solid and use that as your neutral sashing.....
I personally think log cabin would not feature the fabric, something either like a simple nine patch or simple strips.
MSQC has a tute on a block that I think is from the 3 Dudes in Arizona....That is going to be my next quilt....it is pretty, simple but has a little style....IMHO