I would put a used teabag on it to sooth it and if it's still bad in the morning get a vet visit.
Have a good look to see if you can see anything in the eye
By now you've probably seen the vet,but from the photo it looks like the third eyelid is swollen...the eye will benefit from hydrating...use regular washes with a gentle eyewash eg camomile...soak on an eye pad NOT cotton wool which leaves fibers in the eye.
on a daily basis I'd wash the eyes with opthalmic boric acid solution
If she is allergic,consider asking the vet for bentelan or piriton...but also consider having her tested for allergies.