Meares-Irlens Syndrome (sometimes known as Photopic Sensitivity Syndrome) is a disorder related to hyper-excitability in the visual cortex (in this respect it is similar to migraine).
The symptoms that your daughter describes could be Meares-Irlens but there are a few eye disorders that can give rise to those symptoms that ought to be excluded first.
You mentioned that you had already been to an optician but this is fairly specialised work.
Do you happen to be near one of the universities which teach optometry (Birmingham, Bradford, Cambridge, Cardiff, Coleraine, Glasgow, London, Manchester).
I think all of these have clinics that can rule these out and also have clinics to discuss colour-based therapies.
You mention coloured overlays and tinted lenses. There is good evidence that these do work above a placebo effect but the effect can be marginal and depending on how you go into this, the treatment can be expensive.
I think that's probably enough to be going with, feel free to post again if I have been unclear or, more hopefully, you have more questions.