how do I keep track of what skills she is covering and what hasn't been covered? What resources can be used for this?
I don't really think you need to keep track in a formal way. You only have one child to keep track of, unlike a teacher. And you know her well. (Maybe you don't yet know her all that well in an educational sense now, because much of her education has taken place away from you, but you will soon!) Once you've been HE for a year, if you cast your eye over a list of targets and topics, you will be able to say pretty accurately which of those things your child understands and which would be alien to her.
i doubt DD is going to come to me and ask to learn about compound sentences for example.
You'd be surprised. My teenager recently asked me to name all the parts of speech and describe their uses, and she made a chart with examples which she put up on her wall. And this is not an "academic" child. She was just curious. We didn't spend more than a couple of hours on it in total, but I think she understands it as well as the average schoolchild. However, it's highly unlikely that the timing of her interest would coincide exactly with the age the topic is taught at school. So you have to take a long-term view.
If she were to choose to go back to school I would want her to be within a fairly range of the children in her year.
You cannot guarantee that with an autonomous approach. It's usual for a child to be "ahead" in some areas and "behind" in others, because they won't happen to take an interest in topics at precisely the same age the National Curriculum dictates. BUT it is not that hard to get them up to speed rapidly in the areas where they need to catch up, provided that you have a bit of warning. I know a number of parents whose kids were autonomously educated through primary but who then went to secondary school. They just started doing some work in the required areas in Y6.
I personally feel that there is a critical difference between 1) an autonomously educated child who is "behind" her schooled peers in, say, formal maths and 2) a schoolchild who is "behind". The former is only "behind" because she hasn't yet bothered to tackle the subject. She knows she'll be able to do it when she applies herself to it. The latter has years of maths experience under her belt. It is an experience of failure, shame and being forced to do battle with something she dislikes.
People who worry about their child falling "behind" are picturing the latter child, never having encountered the former. Like all children, autonomously educated kids vary. Some children will find certain things harder than other children will. But there's no need to fear these natural variations, because they start from a position of strength and confidence.
Those who are completely autonomous- how does learning to read/handwriting/multiplication (for example) happen? Just curious and excited to hear how it works...
It starts with curiosity, or a need to acquire the skill in order to accomplish something else the child wants to do. It very often starts considerably later than it would be taught at school, but when the child does get his teeth into it he goes at it with enthusiasm and great efficiency, so that the "late" start doesn't matter.
Have you ever watched a child who has been told he has to pick up all the sticks and leaves that have fallen into the garden and put them into the compost? It's hard going, for the parent and the child. It takes ages. Now watch the same child with his friends, rapidly collecting branches and dragging them into a pile because they want to make a den, chattering excitedly all the while. It's fast. No one has to keep him "on task". That's the difference.