100% the queen's sadism is being misled as simple fetish by the MC and his daughter. I think what it really is, is that the cruelty she can exhibit towards condemned prisoners is one of the only times she's allowed intimacy. Death is inherently intimate in nature, and executions are the only time she is allowed to touch a 'filthy' non-royal. The way she comforts Mido suggests that to me, and I think her whispering to him about the "would you use me" was an attempt at a honest and flirty conversation with him before his death. He had to die (even if later on it turns out he didn't) at the moment, but she wanted to let him express his desire of her honestly before she took him. And her comfort of him was genuine.
The kidnapper was explicitly threatening the life of the daughter of the Stalker she admired most, which is why I think she was so hyper-sadist with him, and it's made clear that her using the "dragon" is unusual and rare.
I think that future updates will explore and reveal this more about the Queen, and that she truly doesn't *want* to *have* to be sadistic. I don't think her fetishism of it was something she willingly embraced, but something that came about because - again - it's the only time she's allowed intimacy with others.