Unfortunately I have tried MON's approach with no success, although I am glad it has worked for their situation. The difficulty we had is that a more passive approach was generally ignored or walked over by teachers like this one. It also cost a lot of time.
I think you have tried pleasant and co-operative in your communications with this teacher. Direct and assertive, while remaining calm (and still pleasant) would be my tack, with early engagement of the principal. It was our only way through delaying tactics.
I also agree that you may well need a different teacher as one of your early options because it is very hard to get help from someone who does not want to be helpful.
