Chick sneezing and walks around with its mouth open

My light brahma chick has been suffering what i think is a respiratory infection. She still eats and drinks, but when she chirps, which is a lot, i can hear a vibratin like sound coming from her lungs. She keeps her head feathers puffed up and usually stays pretty cuddled up inside her own feathers and walks around with her beak open. She's such a sweetheart. None of the other chicks have this problem. Theyre about 7 weeks old now, so are fully feathered and outside. Her eyes are also slightly squinted. Anything i can do would be a great help! Thanks!