I think I would try to tuck it in to cover the seam and zig zag over the seam. May not look the best but would keep it from tearing away any more. I would do all the seams like that just in case there are other seams that may pull apart. I would then go back and quilt closer all over the quilt.
Next she needs to buy quilting fabric.
Although some battings say it can be quilted up to 10" apart I never quilt more than 3 - 4" apart. Mostly I FMQ.