For all the reasons cited, thus far. If the eyes are just goopy or watery and not red, it's a plugged duct and usually resolves by the first birthday. Also, have her drip breastmilk in the eye at every feeding. Clogged tear ducts are usually one-sided. A bacterial infection will usually infect both eyes pretty quickly.
Clogged ducts can last for weeks and weeks.
Plantain may be used in place of antibiotics for drawing infection out of the eye. Drizzle a little into the open eye as well. Be sure infusion is strained of all bits of plantain. Works well for pink eye, too. Takes 2-3 days of treatment.