I have experienced positive dysphotopsia and had posterior capsule opacification which was treated with YAG. Neither the dysphotopsia nor the opacification caused pain. I have also done extensive research on both conditions and never saw mention of associated pain.
If it were glaucoma, (a) the pain generally gets worse and worse, and (b) her ophthalmologist would have detected it.
There are a lot of weird things that can cause eye pain, and the fact that her eyes are being checked and given the OK by a real eye doc should be reassuring. He/she would have picked up anything bad that's related to the eye.
However, since this pain always occurs behind the left eye, you might want to take a look at this website:
http://www.just-health.net/Pain-Behind-Left-Eye.html