Lashings of conditioner! My DDs’ hair was beautifully luxuriant when they had nits, due to copious amounts or conditioner.
Thankfully, they only had nits once, when the older one was a teenager. She didn’t mention that she was itching and she had a whole universe living in her hair by the time I discovered them. 😱 Dd2 also had them so I started my campaign against nits with whatever the shampoo is and then did nightly/every two nights combines.
They both had waist-length hair so it was a mission, and even more so when I found I also had nits!!! Gah! Nit World was defeated eventually, though.