Need to stitch in the ditch
 

on a lady's quilt, but she has pressed her seams open. If I stitch really close to the seam will there be issues later on?

If the seam is pressed open then there is no ditch to stitch in. I don't see how stitching close to the seam, but not in it, could cause any problems. Why do you need to stitch in the ditch?

I don't think would be a problem as long as you're catching the fabric from the quilt top and not just the threads, but the stitching won't be hidden in the seam in the same way. If it were me, I would opt for something else. Maybe try it out to see how it looks.

I would explain to her that you can't stitch in the ditch when seams are pressed open, and offer some other suggestions as alternatives.

Stitch 1/4" from the ditch. With seams open all you catch is the thread. Either she re-presses the seams or you do. Do you have the time?

I also had a recent customer quilt that needed some SID around embroidery blocks but she'd pressed seams open. I just very carefully stitched very close,but not in, the seam. I worked fine, but was little tricky!

Once I have batting and backing, stitching in the ditch with seams open does no harm, I think.