Not only did they show the violinist practicing her fingering on her right hand, but the entire episode treated her right hand as the dominant playing hand. While there are a few reverse violinists out there, they are very rare and if she was one if deserved a line of dialogue mentioning it. Even the amputation was to the actual bowing hand and there are violinists who bow with artificial limbs. Given our hero's attention to detail, I can't believe the wrong arm was used for the entire week of filming and no one noticed. If they did, adding a line of dialogue that she was a rate player who uses the right hand would have avoided re-shoots.
Jas is shown at the beginning of the episode practicing fingering with her right hand, which is infected. Violinists finger with the left hand.
The violinist is seen practicing her fingering with her right hand. Violinists do their fingering with the left hand, and hold the bow with the right hand.