It could be allergies or the tear ducts
Why Does My Chihuahua Have Watery Eyes?
It could be allergies, infection or she may have a problem with her eyes! What kind of food are you feeding your Chihuahua? If you are concerned or if your Chihuahua seems uncomfortable, please take your Chi to the vet and have her eyes checked. That would be the safest thing to do! 
I have a 6mos old chihuahua mixed with pom pom and I need to know how many times do they eat and how much to give them..this is my 1st chihuahua,and I am madly in love with him..so I need to make sure he eats the right amount of food and as well and enough food... Thanks