I don't know if this would work for you or not, but you might try some marking pencil removal spray from Quilter's Rule Int'l. I think I ordered mine from Nancy's Notion, can't remember for sure, bur here is the web site
www.quiltersrule.com. Their location is in Waterford, Wisc. I can't say that it works, because I forgot I had it and I haven't used any of it yet. The directions on the bottle does say it removes general pencils and graphite leads, so it may work for you. The markings on your new acquisition appears to be on white, so you probably wouldn't have to do a fabric test first. Beautiful quilt, sure hope you can find something that works for you.