I think we're kinda overstating the amount of hate Valzira has - at least at first. I feel like by the time the dragon meets her at first, her loathing had kinda simmered out, dulled after decades. Every last dragon had been hunted down to extinction, but suddenly a younglings shows up, alone, lost in her cabin. Did she let him go due to some sense of pity? I don't think so. I believe it was all due to her pride (we will touch more on this in a bit). She thought why bother? This newt doesn't deserve the amount of energy required to destroy him. Plus, it'd be far more amusing if his sure demise came by another utter stupidity, then it'll come as a surprise at least.
Lo and behold, the dragon lived.
I don't think Valzira's main trait is her hate, that sounds more like Maelys. No, I think her characteristic and eventual folly is her pride. She thinks she's better than her fellow elves, she thinks she's better than everyone in the realm. She probably chooses to live in a swamp just to not have to deal with her perceived lessers. Then the dragon bests her, not once, but multiple times.
First he beats her in mind by cunningly overcoming her oh so mighty power. By employing the help of some of the other people she thought beneath her.
Second he beats her in body by restraining her and using her as some common whore. A thing she so harshly criticized Heloise of doing, odds are she's never even had such a dirty thing like sex before.
And thirdly and most crushing defeat, he beats her only because she was too prideful to get her own hands dirty and deal with him when she first had the chance. Something she'll think about every second in her cold cell.
I don't even think she hated dragons back then, I can see her viewing them as more of a nuisance and little more. I mean, she even worked with the last dragon for a bit. She doesn't hate dragons, she hates you. But her hate isn't the point, it's the climax, the final stop. It's the comedy of stripping her of her powers, imprisoning her, ripping her limbs off, and using her as a pillow, all to the point where the only thing she can do is throw insults at her captor, all as a set-up to shut her up once more.
So, like I said, Valzira wasn't all hate until captured, then that's all she has left.
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