M.S.
If you haven't called the ER, or hopefully she is better this morning. If the eye is still red and burning, take her to be seen right away. Do not use eye drops that have chemicals in them (like Visine) it will burn like fire, especially if eyes are already burning.
Better to use LIQUID (artificial) TEARS or something designed as an "eye wash". They are a lubricating solution for dry or irritated eyes, they won't burn.
If only ONE eye is affected, I would be concerned that she has something else going on, maybe she has an injury or a corneal abrasion which is really painful. IF both eyes affected, maybe the chlorine, but likely wouldn't be just one eye.