I strongly recommend that you go to see an eye doctor
right away. If you cannot get in to see your eye doctor, then an emergency room might be a good alternative to get a quick eye examination.
The way you are describing the symptoms, which include sudden onset of pain and redness, make the likelihood of a foreign body in the eye, or trauma to the surface of the cornea, very likely. This can occur quite suddenly and often by accident. For example, there are many instances of people accidentally scratching their corneas with their fingernails when raising their hands or rubbing their faces or eyes.
Your eye doctor or emergency room doctor will be able to examine her wife's eye closely, probably using a special lamp called a slit lamp or a special dye that glows in the dark and causes any foreign bodies or corneal scratches to show up more readily. At the same time, they will be able to rule out other types of eye conditions, such as an infection, or acute glaucoma of the eye.
Based on what they find, they will recommend an appropriate treatment, which will likely involve medicated eye drops. Go see the eye doctor right away!