Joyful,

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.

Good luck

Oh my gosh...I've not seen this before and you do have some work to do. The pansies are lovely. I'm sure that you can bring it back to life. Have you considered asking a restorer their opinion?