The fact that Ana and Cora both pulled themselves up by their own bootstraps and both had humble beginnings is probably what drew Cora to Ana. Also, it was probably a strategic move politically to depose of the white king (eventually) and to replace him with her own protege in the nearby kingdom.
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"That’s how you know you’ve really got a home. When you leave it, there’s this feeling that you can’t shake. You just miss it." Neal Cassidy