If she is eating, drinking, pooping, and acting normal, she is most likely NOT egg bound. Egg bound chickens will very obviously be in very poor condition and most likely wouldn't survive 3 days that way.
Do you provide supplemental lighting so that the number of hours of light is the same every day?
Do you live in a part of the world where you are headed into winter and daylight hours are getting shorter each day?
Is her feather condition good/normal?
I suspect it's likely due to the changing seasons and shrinking daylight hours, but any form of illness/stress could cause a chicken to temporarily stop laying. If she seems healthy and normal in every other way, then it's probably just due to seasonal changes and nothing to worry about.