If this scene was ever intended to imply which is Carol's dominant hand (which is dubious; it's honestly pretty probable I'm overthinking this), it's more likely he intended for it to be her left hand.

There's an unused animation of her walking to the right with the guitar in her left hand. This suggests that Toby's intention was for her to use her left hand, but then realized that it would make more sense if Carol used her right hand given her position to Susie in the scene. (credit to TCRF)

Regarding the bit about the knight possibly being left-handed, I'd like to point out something I haven't seen anyone online point out: Carol does initially take Dess's guitar using her right hand and walks to the right with the guitar in her right hand, but when she walks up she uses her left hand.

I think you may be on to something