I would have spoken up, as the customer will be unhappy with the results. That girl should have had some training in cutting and using fabric, even if it was a quick 2 or 3 hour tutorial. I tend to have the cleanest feet in town because I always have my foot in my mouth, but I speak up and even offer advice, which they can use or not. Several times I have helped a customer who asked a question the girl cutting fabric didn't know and I opened my mouth. The customer thanked me, but I admit there are times when I get "the look" and I just shut up at that point. So short story long, speak up.