
Collies are know to have quite a number of inherited eye problems. There is PRA, CPRA, Cataracts (I think) and Collie Eye Anomaly.
Even if she isn't KC registered it will need a specialist to diagnose these.
PRA is progressive, and generally starts with problems seeing in low light (night blindness) and is progressive to complete blindness.
CPRA is a dieing off of the Retina in part of the eye, and is actually a metabolic condition as it is caused by an inability to absorb a certain vitamin, and I believe can be halted if this is supplemented.