The name Cora and the heart chamber suggests she can be the Queen of Hearts. Cora is a miller’s daughter and with that said is Regina that child she had to give up or was there another? If there was another then I’d say The Queen of Hearts and Regina are step sisters. That can explain why the QoH said I am the only queen and she’s just Regina. It sounds like something a woman would say to her sister rather than a mother to daughter. That can also explain the strained relationship Cora and Regina share.