That looks bad. I hope her other seams were more in the 1/4" range. That's one reason I check each seam on the back after I sew them. And, I agree, I do a lot more quilting across seam lines so that if this were to happen, it wouldn't take out the whole seam. So many people only quilt what the batting says is necessary. I look at how many seams I have and the more seams, the more I quilt.
A double sided fusible with glue on one side could be used to do the repair, if there's enough fabric left of the originals. She might need a bit more of one or both of the fabrics, or maybe replace both of those fabrics with a new block. Many ways to do this and most of them are by hand.
Edited to add: Those fabrics almost look like clothing fabric. The weave is very loose. Fabric for clothing is sewn with a 1/2 or 5/8 inch seam. This big of a seam will not ravel as quickly. Loose woven fabric already has a tendency to ravel and the small quarter inch seam isn't enough to keep it together. I have been known to sew an overcast seam over the edges after I sew the piecing seam to keep this from happening. Or, you could sew a zigzag seam after sewing the piecing seam, so that the fabric is less likely to be able to ravel.
Last edited by Barb in Louisiana; 01-01-2017 at 12:23 PM.