Middle School (Mexico City)

I teach at a law school in Southern California. I have a year off from teaching next year (on research leave) and would like to spend it in Mexico City with my 12 year old daughter who will be 13 next year. My daughter is in a very good public school now. I'm looking for a middle school that is either mostly Spanish speaking or bilingual (I would immersion experience for her -- her Spanish is elementary). We are not being sent here by any major corporation that will pay for our housing or schooling. We are not diplomats. So the school has to be reasonable, not 20,000 USD a year. Is there any such school in a nice area, ie Polanco, Condesa, Santa Fe, Coyoacan, etc. Maybe a Montessori school? Any thoughts would be most helpful.