My Dog's eyelid is swollen and pink. What could be wrong?

This problem happened a while ago (like 6-12 months). At first I though it was a bug bite or something.I Put peroxide on it and it went away. Then the other day I thought that there was some eye boogers on her eyelid (a mistake) and I took it off. Turns out it was a scab. So now her eyelid is swollen again. I will put peroxide on it. Does anyone have any clue what could be wrong? It doesn't seem to bother her at all.When I touch it (or nearby it) it does seem sensitive though. If it becomes a problem then I will take her to the vet. Until then, Any advice would be greatly Appreciated.