What a lovely project and sentiments! I too have a wonderful mother-in-law, and a great daughter-in-law too!
I did my first quilt with the serpentine stitch last year, my old vintage machine didn't have the option. I think it's a great solution for any quilt on a grid -- which is most of them. One of my Tuesday group ladies does a lot of preemie and children's donation projects and almost always uses serpentine stitch, and they all look good.