Dirt in the casing?
I would start over and take out the thread and the bobbin. I would give the machine a thorough cleaning (and oiling - if required), reseat the needle, reset the bobbin, rethread and set the tension to its "normal" setting. If fine tuning doesn't work from there, she may have to see the machine doc.
.....and yes, there are gremlins in the sewing room, but they are usually not very patient and leave quickly.
Good luck.