Not once in your long, drawn out narrative did you ever mention checking her credentials! did you actually check that she was a qualified teacher appropriate to the age of your children? However you mention a 9yo and a 15yo - this would mean someone double qualified!!

In future ask at your children's school for recommendations? Or even post on a website that deals with tutors - www.tes.co.uk/forums - look specifically at teaching overseas - its a free website for teachers; Dave EAL cafe (sorry don't know the web address) or one of the expat websites.

Hopefully lesson learned!