Viola really doesn't understand what the soulmate means to the Demon Lord, Noche in particular, and it shows through her upbringing; she's not yet managed to grow out of entitled brattiness in 800 years of life. Understandable, I suppose, considering most humans who end up that way IRL don't grow out of it, either.
However, I imagine Noche is going to make her spontaneously explode or some such for pulling this shit.