I mean she does say she needs to look the part for future negotiations. So she doesn't want people to look down on her as a gang leader that doesn't dress well.
It's either that, or because her body was born under the "star of misfortune" it may just be that since she has the mind of an adult she really is able to control the "madness" that Zenon mentions in his report to the duke that he showed Viola.
I really don't get the hate people have for him using ranged magic in a mech. Adventurers and soldiers use bows and offensive magic surely, so why is it so looked down upon here? doesn't really make sense...