I also wouldn’t discount the fact that Regina hasn’t done anything to directly harm Emma because of Henry. In all the interviews I have seen with Lana she has always said that she plays the part being very aware that Regina does love Henry. So keep in mind that although she hates Emma, she does recognize that she is Henry’s birth mother and that actually doing something to harm her, especially to kill her, would devastate Henry. And she is aware that her son believes that she is the EQ, so harming or killing Emma would only make her relationship with Henry only more strained than it already is. Not having seen enough of her backstory yet, I don’t know what happened to her early love. But in FTL she killed the thing (her father) she loved most of all in order to inact the curse. At that point it seemed that, not only was her father the thing she loved most of all, but her father seemed to be the only person who loved her. In Storybrooke, Henry seemed to have been the only person who had the potential to love her – appearantly that wasn’t going well even before the book came along. Then when Henry got the book he became convinced that his mom was an Evil Queen. Since time stood still in Storybrooke before Emma came along there wouldn’t have been any reason for Regina to have needed to use magic. But once Emma came along I think the threat of losing Henry, the only person who seems to have the possibility of loving her, could be the reason she hasn’t used her power/magic in obvious ways . . .yet.