My parakeet who is under a year has overnight somehow gotten one black eye, is she sick?

She seems to have developed this over night. She is missing the feathers around one eye and it looks black. I feed them strawberries, and lettuce often. I also spray them with water to entice them to bath themselves. They also fly around the room throughout the day. Do I need to take her to a vet tomorrow or will it go away? She has vision out of it. Why does this happen?