You don't help by describing this teacher as hostile. You presumably have only seen your child - she will have seen many children. If your child is in a state school, then there will be other children in the class who have just as much right to her attention as yours does.
Who said he was 'officially 4 years ahead?' He is little fgs, let him learn at his poce as opposed to hothousing him too soon.
My ds hated Oxford Reading Tree, was bored brainless with it, whilst reading much more 'advanced' books at home. The problem with bright kids is that they won't demonstrate what they can do in order to get the boxes ticked, and that can create problems. There is no point setting a child a piece of work at GCSE level when in Year 8 about the pneumatics of how a meander forms, when they won't even show that they know what a meander is. It may well be the same problem here.
The teacher wants the best result for each child in her class, but will not respond well to being called hostile, any more than I would. She knows her job, either let her get on with it or work with her, but don't put her back up.
MWITA - I used to get some of the brighter kids to teach things to the weaker ones. It helped me judge their level of understanding and grasp of the subject (you only really know it well if you are teaching it), to correct any misconceptions, and to help the weaker ones.