Get Pet Questions Answered by Pet Experts
Until you can see the vet, you should flush the eye with saline and then dry it well with a clean, dry cloth.
You might be seeing the third eyelid. It only presents itself when there has been a trauma to the eye or the dog has an eye infection.
If the saline doesn't help, you will want to see your vet for a diagnosis and to discuss your treatment options.
If there is an infection present, your vet will probably want to get the dog started on antibiotics.
While it's not an emergency, you don't want to let it go too long, either. Can you move your appointment up?
That's pretty much all that you can do at home. I would try to keep her calm to prevent damage to the eye and see the vet as soon as you can.
Let me know if you still have questions.
Are you sure that she's not having an allergic reaction that it causing the swelling and droopiness? A bug bite, maybe?
If you suspect this, you can try a dose of benadryl. My vet recommends 1 mg per lb of body weight given every 8-12 hours as needed.
I hope this helps more!