Katymac - I also have a Jamaican/British daughter, but she's only 3 and her hair took ages to grow in so I'm at the beginning of trying to work out what the hell to do with it! I can imagine when she's 13 and has much longer hair it will be a challenge. So I don't have the answers - only more questions for you!
Firstly, I just wondered why you did the defining twice in your OP - I thought it would only need to be done at the very end of the process? I've probably missed something from the website as my 8 month old is still waking constantly and my concentration is shot!
What method are you using for defining? I tried the "doodles" (wrapping chunks around my finger and twirling) for the first time yesterday, and it looked amazing. But she's just got up this morning and it is a mess - not so bad as I'm still on mat leave and have time to sort it before we go out, but I won't be able to do that when I'm back at work and in a rush to get her to nursery.
Does your DD sleep in a silk cap/on a silk pillow? I've heard lots of people mention this, but haven't found a child-sized cap in any of the hairdressing shops I've been in (and always have the kids with me so no chance of having a proper browse!) And does she put her hair in twists or plaits for sleeping? It's always the last thing I can be bothered with before putting her to bed, which is why I've been practising corn-rows and twists, so I can do it once and then leave it for about 4 days. But I would love the option of easy "down hair" - I'm not sure it exists though!
mamaesi - I was concerned about using adult products, too, and tried a few of the products specifically for mixed race children, but they were really expensive (and still full of chemicals). I saw lots of mixed race hair websites recommended the blue Herbal Essences conditioner (Hello Hydration) so I now just use that. I use it to "wash" the hair, rinse out and then apply another big dollop that I don't wash out. I know the tightly curly website doesn't recommend it for keeping in the hair anymore, but I've yet to find another product that works as well as this one. And it's cheap and smells lovely!
Wow, that was a long post about hair! I think I need to get out more!!