In Natasha's view Cassie had gotten it spot on and went to show how much her daughter understood her. It meant a lot to know that despite not liking the superhero background she had still included it within the design. It was a big part of who Natasha was today even if it had led to the circumstances of her death back home.
Considering Natasha pulled her shirt over her head, "Would that work?" she asked, indicating her right shoulder. Other than a couple of scars she was pretty much a blank canvas for Cassie to work on. And there was no worry about her being able to sit for a couple of hours, Natasha had kept still during interrogations a number of times no matter what had been done to her. Tattoo needles wouldn't be an issue. Especially since it was her daughter wielding them, someone she trusted implicitly.