Night terrors and starting school full time - advice please!!

[cerysb]

Hi
We have been dealing with my 4.5 year old DD's frequent night terrors for more than 6 months now, and managing them with reasonable success by attempting to stick to a routine of a decent nap (45 mins ish) during the early afternoon, and she goes to bed around 7pm. There are inevitably days where she either doesn't get a nap, or only manages a short, poor-quality sleep in the car, and when this happens, the night terror is pretty much guaranteed, but obviously we can't stay at home every single day so I can't see how to avoid this.
Now she has started school, and as she is a summer birthday, she is currently only doing half days, so we can still manage the afternoon nap. However, as of after half term, the teacher suggests we start to build up to one or maybe two full days (until 3.15pm) per week as in January she will be expected to attend full time every day.
I agree in principle, but am very worried about how this will affect her sleep. Has anyone else had to deal with a similar situation to this, and had any sucess managing the overtiredness?
Any advice really appreciated.