No, I figured she had some not so nice secrets when she opened a portal in the floor in the first book.

I think she is still nice at heart, she just has some bad views on the world which has caused her to do bad things.

That's because at first there was a Curse preventing the prince's from telling Emilia who she used to be, so as a work around the Curse they would mention the "feared" to her as if the feared were something else entirely and not just her and her sister. So Emilia and Vittoria are the "other hell gods" its just at the time no one was physically able tell them that lol.

Vittoria and Emilia were the feared, referred to that way because they were bored immortals and so they apparently did heinous things because of that boredom