Easiest fix for a split seam after washing?
 

My friend is struggling with a small lap quilt. After piecing, quilting, washing, and drying she now has a large split seam. Minky used as backing. Unknown for batting. I dont think it was quilted enough since I can see the backing. Easiest/best fix for something like this?

I would hand stitch it together. Seems her seam allowance was too narrow and maybe the stitch length was too short almost cutting the fabric.

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.

I watched a really informative video by National Quilters Circle (Heather Thomas). She recommends quilting 1 inch at the most apart for a quilt that can withstand routine washing. May not be what everyone recommends, but she believes the close quilting contributes to the longetivity of the quilt.

https://www.youtube.com/watch?v=eSJNVkKjHv4

I think Barb is right about the fabric being not the best choice for quilting. Looks too soft.

Also looks like the batting is all coming apart.

if she has extra of both fabrics, applique a new pair of fabrics over the existing ones. that will add a layer to stabilize that torn seam.

Tartan's solution sounds best--but think she also needs to think about NOT washing this quilt--and maybe add more quilting.

I would be concerned that this could happen again in a different location, unless the quilter takes steps to make sure the quilt has been quilted properly.