Um, Sue didn't cut her hand. Mel did that to her. They got into a fight and Mel shoved her into a glass frame that permanently damaged her hand so she can't operate.
It was accidental
If you read the new chapter, Sue did cut her hand out of jealousy, she made it even worse. Yes, it wasn't like that before because Mel accidentally injured her hand and now she can't operate anymore because of Mel. Maybe you just read the comment wrong and assume that they were talking about before but I think they're talking about the after.
There is nothing in the new chapter that indicates that she cut her hand. She picks up the scalpel in her right hand, the injured hand, you can see the scar. She tries to hold it in her injured hand but her hand starts to shake and she drops the scalpel. She stares at her injured hand in frustration. The way it's drawn does not look like she cuts herself IMO.
Sue might be jealous and into BDSM, but that doesn't mean she's a self mutilater. She wants to be a surgeon and carriers her surgical instruments around as a what if. Probably takes the instruments out periodically hoping she'll have the control of her hand. At least that's how I interpreted it and I could be wrong. Read the chapter a few times and it doesn't look like she cut herself at all-no blood and why would she cut her uninjured hand?
My bad, I've read the chapter a few times as well but it would be sick if she would have use the scalpel on her injured hand but rereading the chapter, I fully understand that she was just trying to see if she can handle using the scalpel since she wanted to be a surgeon.
Regardless, she's still messed up in the head to purposefully cut herself out of frustration over an old lover was my entire point. No one should have to go through that and I'm hoping she doesn't shove the scar in Mel's face as a means to guilt trip her into thinking she "did that to her". Sue's just a scorned manipulator and that's dangerous given Lynn's in the middle of all this.
I was thinking Sue's hand was gonna look like melted pizza cheese or mostly muscle or something... ┑(￣Д ￣)┍ She's one sick motherfucka tho, cutting her hand like that... "The jealous are troublesome to others, but a torment to themselves."