She knew they thought she was weak because they didn't back down, and Nessa was already in a bad mood and didn't want to waste her time with them.
Nessa was not the type of person to brag about her abilities that others do not have because she does not believe herself to be all powerful. She knew she had a lot more to learn and that she was not even close to reaching her full potential as of yet, which is one of the reasons she was cautious with her abilities.
"I am going to give you guys one chance, I am really not in the mood for this right now, so I suggest you leave while you still can," Nessa said and the guy gnashed his teeth and released the fireball he created and before it could touch Nessa, she dodge it before disappearing then reappearing behind him and kicked him to the ground and the others looked at her.
At the same time Yonja and the others arrived at the guild and since Nessa was nearby the saw and they left staring at her.