Look up how people talk about recruiting Mithera in BG3 if you want a good example of how sometimes the simple solution in game design is the best option.

I get the initial intent was to make her exclusive to an evil playthrough initially but also what the fuck did you think people were going to do when you offered a drow baddie? Of course they were going to exploit the hell out of your needlessly complicated systems! Just use basic event flags when you patch her as viable!