Does Humpty stay with another hamster? If she does, perhaps the eye got scratched during their play. Otherwise it could be something that irritates her eye. This could be dust, beddings, etc.
You can help her by cleaning the eye with boiled water (slightly warm, NOT hot). If you have CS, drop some CS onto the eye. Do this a few time a day.
If it is just a irritation, the eye will heal quickly. If problem persists, best to consult a vet.
If the problem recur, suggest that you identify the source of the problem. Change beddings for a start.
Hope this helps.