Even though Charles treated Disa cruelly and eventually banished her to the house where she grew up in the south of France, Disa clearly still cares about him. The revolution worried her tremendously, and she offered to shelter Charles and tried to rescue him, even at risk to herself. Furthermore, she cares about him enough to know his voice even when he’s in disguise. It’s clear that King Charles doesn’t deserve any of this love or attention based on the way he treated her, but Zembla is a mirror world that reflects Kinbote’s ideal life. Kinbote is a misogynist who believes that women owe him unconditional support and cooperation (he believes this of Sybil, for instance), so in some sense it’s no surprise that this would appear in his fantasy.