‘Pet’ lamia for an NPC

Is there any spell/item which could turn a lamia (the snake ones) into something house-safe? Preferably not an outright slave, but evil tendencies inhibited. Mustn’t require the NPC to be a caster. Cost no issue as NPC is well resourced, but shouldn’t be as rare/overpowered as “wish”.

NOTE – I’ve realised snake-lamia aren’t an official species. I’d been looking at the stat block at https://www.5esrd.com/races/3rd-party-publisher-races/kobold-press-races/lamia/, but I’m happy with any similar seductive-but-evil type race, if that helps.

Background: I’m planning an NPC politician who I want to give a slightly unsavoury feel to, without having them doing anything overt like running around killing people (depending on how the campaign develops, I’m planning they could turn into a populist leader who may or may not turn out to be evil). The NPC will be friendly towards the PCs. So I want some unsavoury flags that will suggest to the PCs not to trust them, without anything overtly illegal or that the paladin will immediately feel compelled to jump in and resolve. So I’m thinking of a “trophy wife” lamia or something.

Frame challenge or other suggestions also appreciated.