Your original idea should work just fine. I have done just that on several quilts. Back when liquid embroidery was popular I made a quilt for my then infant daughter out of blocks I had painted. I used cotton batting and didn't quilt it close enough together. The first time I washed it I had a mess. I had to completely take it apart, use new batting and quilt it much closer together. Since then I have done the same for several quilts for other people. One I even had to replace some of the squares that had just rotted away. It was made of feed sacks. I was fortunate enough to find an apron made of just the right color feedsack that was in good condition. It provided the fabric I needed for the repairs.
Your quilt is lovely and since your Mom made it I certainly would repair and restore it if I were you.