I would loosen the upper tension all the way, then use ***unwaxed*** dental floss to try to clean out any lint that may be caught between the tension discs. This is assuming she can reach the tension discs. Not sure if that is possible depending on what model of Singer machine she has.
Edit: And presser foot should be in the up position when doing this so that the discs are not engaged.
When threading the machine, she needs to make sure that the presser foot is in the up position when seating the thread. She may have tried to thread the machine with the presser foot down, which can prevent the thread from seating properly.