Some brainstorming --- Can you show her how to chain piece and only cut the thread at the end of a whole bunch of seams?
Is the thread getting caught anywhere on the fabric as she puts it under the presser foot?
Is there an auto cutter? Or even a manual one on the side of the machine? Are you using that or scissors? That usually requires a longer tail than scissors.
I have an Elna (same manufacturer) and DD has a Janome Gem and for us it is just usually that the thread tail wasn't long enough.