After knowing the truth behind her mother’s death, she decided the only way to stay alive and perhaps take vengeance is to become the heiress or the mother to an heir. If she is important enough to the King, she would be protected and could get away with anything, even if that means killing the Queen. So that is exactly what she did, while eliminating every other possible heir, leaving herself (or her child) the only choice. Whatever innocence left in her is lost in the bloodshed, so what happens in this flashback is no justification for her cruelty, she just isn’t the same person anymore. No forgiveness here.
As for why she kidnapped and raped Raoul, the blame is certainly on the Goddess, partly at least. However, as common plot points go, hypnotism doesn’t work if there isn’t already a hidden urge. If I have to guess, by the time she met Raoul, she is already corrupted by the ways of a cutthroat noble, climbing her way from irrelevance, threat of death (presumably from the Queen or other heir aspirants). The sincere and innocent eyes of Raoul, the hero, pursuing the betterment of mankind, symbols of justice and the good. They must have reminded her of something she thought doesn’t exist, a pure heart, something she lost. That’s why there was this urge to be with Raoul in the first place. Unfortunately, that love was amplified by the Goddess, and subsequently misdirected by her corrupted ways.
One thing I notice in her motivations towards Raoul is that: It wasn’t just bodily desires or the want of an heir, as you see in what the King did to Valentine. It was love, albeit twisted. Twisted by her possessiveness, though I believe that was force of habit. By that point, one must wonder: What kind of person is she by the time she meets Raoul? Well, I don’t remember the Queen being there in the early chapters, so that might be proof that she’s already dead. I remember Victoria claiming that every other heir apparent is already dead as well. We thus can conclude that she is already a cold-blooded killer at this point in time. Not a psychopath who revels in the killing, no, just someone who is willing to use any means to get what she wants. Now, take that way of acting, and give it an end, amplify it to its strongest. Finally, the product is what we all remember and hate, that is what Raoul remembers.
And now we know at least the clues of how Victoria got there. That is not cause for forgiveness, but wouldn’t you think: For who is supposed to be the main girl for Raoul, it would be too shallow for her to act in evil just because? That, and for Raoul to create the perfect world, it would help to understand how evil is born in a once-innocent person such as hers. Who knows? Maybe he would enjoy knowing more about how Victoria his rapist came to rape him.