What a dilemma Dinky.

Well, maybe Tayla's new teacher can spot these issues because he is new and is looking on the problem with fresh eyes? I know that some kids who are very bright will deliberately not work in order to avoid bullying for being the 'nerd' or 'brain'. You say she is a great manipulator so she may be 'playing dumb' to avoid being singled out for bullying to the detriment of her grades.

I think pulling her out of school and dropping her down a grade may be a bit drastic at this stage. Talk to her OT, maybe they are glossing over things for you. Or have her reassessed again with a new OT? Does her school have remedial programs? Maybe a 3-way interview with Tayla's teacher, yourself and Tayla might help sort out any issues she is having.

I hope you find a solution soon.