I have some of that kind of thread. Notice that it says (embroidery). It is not for quilting. I have also used a gold thread from Superior Threads. The weight I used was 40 and it was King Tut. It worked very well and looked beautiful. I cannot help but think your customer wants the color she supplied. She may not understand the characteristics of various threads. I think you need to be honest with her and/or show her samples of quilting with various threads. If you know that this will not work properly, why continue and have a poor finish. Speak up.