My DC learnt a musical instrument from this teacher at primary school. She sometimes displayed a lack of empathy and that seemed to cause irritations to the parents (and the pupils). But I always chose to trust her and supported her.
However, suddenly I realised, she really was very toxic. She often talked about her ex-husband bitterly and painted him as some sort of a monster. But ironically, she was treating her pupils and the parents as her ex was treating her to a certain degree. She was unnecessarily mean, judgemental and cynical.
We stopped her lesson a couple of years ago so we have been out of her influence for a while now (though we are still in touch with her for various reasons). I just cannot believe how come I managed to ignore the signs of her dark side. I wish I recognised it earlier. Plenty of damages have been done.