I have two featherweights and take care of about 6 more. For piecing, I always recommend the foot you described and the piecing foot that came with the machine, depending on whether I am sewing on the edge of the piece or not. I find that if my seams are pressed well, I don't have many problems going over them with the guide foot. As for your sister's feed dog issue, has she removed the needle plate and cleaned the feed dogs? They are much less effective if there is a lot of buildup in the grooves. An old toothbrush is great for cleaning them out. Have fun!