She needs to listen (or have a friend listen while she sews) to find out where the clunking sound comes from. I suspect it's coming from the bobbin case. She needs to take it out and clean and reclean every little nook and cranny..use a business card to clean out the small openings in the bobbin case...then oil well. Remove the upper thread and let the machine "sew" at a medium speed for a few minutes to distribute the oil..then check again for any lint that shows up. Another area a lot of people miss is the feed dogs themselves..they can accumulate a ton of lint in them.