Shawn is a habitual line stepper and desperately clinging to relevancy. But yes, "sis" is commonly used among Black women as a term of endearment, and it's super cringe she used it with her two Black colleagues. Also, younger women DON'T call our elders "sis". It would be considered condescending, similar to "sweetie" or "kiddo". But Shawn lacks awareness, and she's not Black, so of course she'd pick up the wrong phrase then proceed to use it all wrong.