I love Lancer & Susie’s friendship, so I was quick to wonder if this scene with Tenna was an intentional callback to that, as it didn’t really make as much sense for him to refer to her that way otherwise, unless whoever he was talking to didn’t recognize Susie by name. The circumstances are very similar too, it’s when Susie realizes that the person she’s just connected with is working behind her back. It feels more cold when they don't refer to her by name.
And yeah, both Lancer & Tenna are characters who get along with Susie right off the bat and aren’t put off by her abrasive comments. They also try to appeal to her personality, instead of challenge it. (Lancer with genuinely taking her advice and trying to mimic her, Tenna with making a minigame just for her themed around her wish of being Susiezilla.) She fights them both when they betray her, but she also opens up more because of it, and ultimately she wants to help them in whatever way she can.
I sort of think of them as the Dark World reflections of her connection to Kris & Toriel (although they are very much their own people with their own dynamics with her.) Weird kids who look past her bullying and want to befriend her for who she is, and friendly adults who don't take offense to her and want to make her feel welcome and valued.