She comes by almost every day now.
First seen here https://mostlyphotos.wordpress.com/2011/10/09/white-hummingbird/
She is leucistic. Leucism is a genetic mutation that prevents melanin from being deposited normally on feathers. Leucistic individuals have melanin in the body, giving dark eyes and colored soft parts, but the melanin does not enter the feather structure and the plumage is white, whereas albinistic individuals lack melanin in the body as well as the plumage.