Colour code things as much as possilbe - work out colour systems. It makes a world of difference. It doesn't sound like dyslexia,but it could be some other from of processing issue. My son has significant disablilities in this area and colour coding has helped him so much in school and routines. Using other visual cues (little pictures and icons) also is very supportive.
It still might help to use different coloured paper for the music as well - maybe cellophane would be cheaper and easier because you can use it to cover pages successively - instead of having to copy everything in advance. Try a range of differnet colours and see if she finds any suddenly easier to read - she shoudl be able to tell pretty clearly, like an "aha!"
Try using pictures on the piano for a while, too - like a down arrow at the lowest end of the keyboard and an up arrow at the highest end. Anything that is a particular problem, find a viaul cue to relate it to.
I wouldn't say anything to the parent/s until/unless you find some particualr strategy really makes a difference. Then you could say you had observed this and that worked. Then, you would be in a better position to suggest an assessment - since professionally you are not in a position to do more than that.
Good luck
Annah