My baby has this as well.
Stop washing hair so often to start with, and don't put so much different stuff on it. You need a routine of using one or two products only and then give it time.
Bath and wash her hair once every 2-3 days. Use an eczema friendly shampoo, I recommend the Child's Farm oat one. Don't use bubble bath and limit time in the bath, 5 mins or so, just washing and then out. The bath water itself is actually drying, even without any products in it, so you want to limit the time she's in there.
Cover her scalp in epaderm cream (not ointment as it will totally gunk up her hair) after the bath, before bed, and as many times each day as she will tolerate - I was literally doing it about 6-7 times a day with my son - now it's under control I do it morning and evening.
Don't rub it in too much and apply it in the direction of the hair. It will soak in.
Definitely don't use coconut oil or other oils - it won't help with eczema, it's more for cradle cap which is a different thing.
If she is really itchy you could use Aproderm colloidal oat cream before the Epaderm. I layer it - a layer of oat cream helps the itch, then epaderm on top will moisturise and seal it in.
You can get Epaderm cream on prescription for free.
Don't use Aveeno/ Weleda/ other high street creams - they are not really good for baby eczema despite the claims. Just use emollients like Epaderm/ Aproderm which are actually proper moisturisers for eczema with fewer ingredients.
Good luck, it's so uncomfortable for the little ones!
We also give our son piriton at night (on doctor's advice) as it also helps with the itching, I would recommend seeing GP before doing that though.