My sister was diagnosed with allergic conjunctivitis and has had it for the last several weeks. Her eyes occasionally swelled, but they remained white instead of pink or red. In the last few days, my sister developed severe ocular pain, more painful swelling (no bulging), and eye watering (clear). She followed up with an ophthalmologist and took their directions, but there's no help.
What can possibly cause my sister's eye swelling and other symptoms? Could this be an infection?
If it's a hereditary allergy, what steps can I take to avoid developing similar symptoms?