It seems that Eva wasn't always a nice person choosing good over bad and being the adored queen that she was before she passed on and Regina took over. In the end of this week's episode, we hear Cora standing over the queen's lifeless body claiming that the reason she did it was because she never wanted her daughter to know what it felt like to be the daughter of a miller. While Regina seemingly never grew up that way, it seems that her mother wanted to make sure she ended up as royalty.
While Cora likely was never a saint, it seems that she may have been the brunt of some of Eva's plans or work that she didn't enjoy. This could be the reason she has such a bitter taste in her mouth of the Charming family, but Snow is planning on turning dark and doing what she feels in necessary to keep her loved ones alive instead of simply doing what is right and expected of her. Cora could have an epic battle to deal with that seems like she could be on the losing end.
In the sneak peak photo shared with this article, we see that Cora made some kind of deal with Rumpelstiltskin. The real question is why and what was the deal over?