My daughter has light green snot, so much she can barely breathe. What could it be from and what can I do, shes 18mo. Teething. Tiny fever. Nothin els?

Allergy. Light green sinus mucous is often indicative of an allergic process rather than a bacterial infection. In younger patients, bulb suctioning can sometimes help clear the nasal passages.
Call the doctor. Since your daughter is having difficulty breathing it is time to call your doctor. Runny noses frequently happen when babies are teething but when there are breating problems and green snot whe needs to see a doctor.