Deteca being able to Voidmake is a good way to see the core of her character development. Voidmaking is using the Void to just destroy stuff. It's not technically evil, but since hardly anyone can do it and those who can are DA, Deteca thinks of it as evil, like Hemalurgy (though that's not precisely evil either, and she somewhat knows that, but it's hard to get rid of prejudices). To me, the significance of her being able to use it is in the contrast. It's just another magic system, but it's one that my character sees as being wrong, and she sees herself as a good person, since her guild was basically founded to do good and be opposed to the Dark Alley.
What she needs to do is find the contrast, recognize that gray areas exist. OOC her development is a way of saying "Yes, we all have our own guilds, but loyalties aside, none of us are perfectly good or bad." Morality is a spectrum, and it's a very subjective one. This is also why I’m going to have her be a DA Denizen in Era 5; the symmetry of having her grow up in that guild rather than TUBA appeals to me. Neither are perfectly good or bad, but she has to figure that out.