Like the other characters from Castlevania: Grimoire of Souls, Hermina's story suffered from the cancellation of that game. Pitched as the villain of the game -- the one who stole the titular grimoires and then used their power to tap into the darkness of Dracula, it was possible that there was more to what was going on. In all fairness to the character, she could have been a secret hero, like Albus before her, someone who was trying to actually seal away Dracula's power, even if it didn't seem that way at first blush.
Introduced near the end of the fifth, and sadly unplanned final, chapter of the game, Hermina arrived with a seemingly brain-washed Soma Cruz, with the heroes assuming she was controlling the hero so she could steal the Grimoires and use their power to resurrect Dracula. Three more chapters, though, had been planned, and the true story of Hermina, and her goals in the game, were never revealed.
What is known is that Hermina was the first to discover the true power of the Grimoires and that she was the one to steal some of the books from the Order of Elgos (which, it should be noted, has a suspicious similarity to an alternate name for Eligor, a Duke of Hell featured in the series and this game specifically). She then used the magic of the books to alter the timeline, seemingly to wipe away the heroes that defeated Dracula all to empower the Dark Lord.
As noted, though, it is possible that the true villain of the game wasn't Hermina but, instead, the leader of the Elgos, Seward (in a heel-turn not unlike that taken by Barlowe in Castlevania: Order of Ecclesia. Although it's just speculative to say at this point (as the release notes, and future plans for the game, have yet to be released), its entirely possible that Seward could have been working on the grimoires and everything Hermina did was to prevent his efforts to raise Dracula, even if the heroes didn't yet realized it when the game was canceled.
If that were the case that would mean that Soma had teamed up with Hermina after she convinced him of the good they could do, and it would also mean that a massive twist was due in the game by the later chapters. We likely never will know, at least not until some version of the game is released in some way so fans can see what was due to come out and where the story would have actually concluded (had it been finished).
For now, then, Hermina goes down as another villain of the series, someone looking to tap into the McGuffins of the series for her own evil needs. We'd like to think there's more to it but until someone associated with the game lays out the details of the final chapters this is all we can know for sure.