Ps 150

I know it seems silly, but I'm trying to fix a store bought quilt. I bought a cat quilt for my cat loving daughter before I knew how to quilt. It was her first quilt and she's very attached to it since it was hers since she was a toddler. The seams are breaking, though, and exposing the batting. I offered to make her another like it, but she really wants me to fix this one. I've tried to do a whip stitch, but these cheap fabrics aren't holding them very well. How would you suggest fixing it?