I’m sure Nev will eventually chime in but I don’t think there really is a way to achieve this exactly, especially because of the scar issue like you mentioned. I think you could either just make Rey scarring Kylo happen quickly after she connects with the Force. Or, just find ways to emphasize Kylo’s injuries more, to clearly express that Kylo isn’t at the top of his game when he fights Rey.
Nev I think is also approaching it like Rey is tapping into the dark side to get the edge over him, so she beats him, but it is sort of ominous because we know that she is on a precarious edge. She has yet to learn how to differentiate the light and the dark, which would raise the stakes for her to learn from Luke.
This is exactly right, and somewhere I did a mockup of the traumas of her past bubbling up when she draws on the Force. To this add the sinister whispers I added to Rey shooting the Stormtrooper at Maz’s castle and her successful escape attempt, and it should serve as a fully-developed concept. Rey is being seduced by the Dark Side, even if she doesn’t recognize this easy power.