Shih tzus are a breed of dog that has eye problems. At age twelve, she could have glaucoma, dry eye, or irritation from hair getting into her eyes. There are several tests that your veterinarian can perform to find out what the problem is. Good luck.
Shih Tzu's are one of those breads that have eye problems. My Shih Tzu's also have this discharge from the eyes. Best to keep the eyes clean so clean their eyes with a warn cloth every day to stop a buildup under the eyes which matts the hair under the eyes.
If you are worried about it contact your vet!
If you are worried about it contact your vet!