Left, or Something Like It

So, now I'm genuinely stumped with a couple of my students. Both of them, to one degree or another, are starting to have serious problems telling their right hand from their left. The first one I'm not as worried about, because he doesn't do it when he's relaxed. It seems like he gets stressed and defaults to playing with the right hand (or, if I ask him to move his left hand, he almost always moves his right hand). Not a huge worry.

This other one, though, the girl. So strange.

She will transpose a line of music (to the correct set of notes! this is what blows my teeny little mind!) from the left hand to the right hand, or from bass to treble clef if you prefer, and back without batting an eyelash. I cannot for the life or me figure out where this habit comes from. It is because they are used to using just one hand at a time for the duration of a piece? Am I making them that nervous?

Granted, she is coming to me from a couple of years' experience playing the clarinet (nothing else before that) so the concept of reading one line at a time is throwing her for a loop. Perhaps running back to a "single line" mentality is begetting this hand switching. The one-line thing is funny, too, by the way. Today she kept pausing in the oddest fashion, in strange places, and I finally stopped her and I'm like "Child, why are you stopping?" And she said, "I'm counting the rests!"

Sure enough, every time she got to the end of a line [in the treble clef] she went back to count out all the bass clef rests that had been going on during the right hand melody, as if each individual line of the grand staff were to be read like single-line band music.

I'm figuring it out. One half of my brain at a time.