Leave it in. You'll get a rhythm for what works and what doesn't in her hair. Old school used to grease the scalp, comb through and then style using braids, plaits, leaving it in a 'fro', bushballs, or other. New school realizes that anything with mineral oil or petrolatum does not allow the scalp to breath, so new school uses all natural hair 'grease' or oils to lubricate the scalp and hair. This is done because afro hair texture does not allow moisture and the natural oils from the scalp to coat the hair as easily as straighter hairs do, so we enlist the aid of natural oils. This is why we don't rinse them out. They help lock in the moisture and coat the stands. Brushes are BIG no no's. They tear our hair. Use the tangle teaser as a brush and a big fro comb that won't tear the hair.
Go lighly when you oil, you don't want a grease ball on your hands. I'd say washing every 1 or 2 weeks is enough. In my household, we co-wash each week, which is washing hair with conditioner. It doesn't have to be WEN, it can be ANY conditioner you like. You can use shampoo maybe once or twice a month to keep from stripping the hair.
To keep the hair ends from drying out, I recommend acidifying the hair once or twice per month using Roux 233 Porosity Control Corrector and Conditioner.
When you cover the hair at night it should be with a silk or satin scarf. Or you can do it the easy way by only using satin pillow cases. The keep the oil and moisture from being sucked out of the hair and help cut damage WAY DOWN!
I visit the forum only once in a blue moon so I hope what I posted helps you in some way, just in case I don't log back in for a while. The other sista's who frequent will probably chime in with more indepth advice.