That is a gorgeous quilt and you did a beautiful job piecing it!
I'm going to be brutally honest here. Stitch in the ditch is actually the hardest thing to do, especially for beginners.
I understand your friend's desire to let the piecing stand out, and I think that's the right thing to do with this quilt. But I think you can accomplish that easily by:
1) Use a large, open panto. Don't choose anything that is quilted tightly or closely.
2) Use a finer thread, such as Bottom Line (60 wt) or Microquilter (100) wt. This won't show up as much as a heavier thread (most quilters quilt with a 40 wt thread).
3) Use a color that will blend in, such as a pale gray or pale blue.
At least, that's what *I* would do. 😉