DD1 has thick, wavy hair, curly when she was a baby had no hair to speak of for five years and I got the best advice from a woman who ran a store selling Afro and European beauty products.
She said that I should treat her hair more like natural Afro hair than European, even though it fairly obviously wasn't (bright red) and -
Condition every day with an extremely light, well diluted conditioner, mixing it with water in my hand before applying it a bit at a time.
Sleep in a French plait.
Take it out each morning, spray it with a light, oil in water, product and then take tangles out by laying the ends of the hair in my hand and just detangling the last inch before working backwards to her scalp.
Put it back in a French plait for school to avoid nits being able to get to her scalp - they'd only be able to reach around her ears, etc, by the time she got home, so I'd only have to worry about them there, rather than having to do the whole head.
Tea tree oil is too drying. Use Lavender and drop 5 drops around her crown, forehead, ears and nape of neck, give it 2 minutes and they'd all run to the surface.
Never use nit shampoos/products. If any emerged from the Lavender oil, soak it, add diluted conditioner and go back to the combing through just an inch at a time.
Use a very light, pure shampoo, not a greasy/super moisturising one, as she needed a clean scalp, but the conditioner would stop it becoming a problem. Use it by putting a bit on my fingers and gently put directly onto the roots, rather than applying to the hair and hoping it reached there through rubbing hard/adding tons.
Wrap a towel around and squeeze dry, never rub dry.
Do it every day, as it only took missing one day for the loose hair to mix up and for it to start to dread.
Her hair looked great once I started that and I never needed to deal with a full scale nit invasion again.