Can you be a bit more specific on whether she can reproduce the lower jaw pain by rubbing tongue on the upper or lower teeth? Also can you comment on what treatment approach you have done already that has lead to the reduction in episodes. This might assist to give more light to a continued treatment plan.

Perhaps a second dental opinion might also be of assistance as I have had this when eating intermittently due to worn enamel on the surface of a back molar. This simple became sensitive. Maybe the night splint is letting this slowly heal and that is leading to the reduction in painful episodes?