Isolate her with only water and observe her for a couple of hours or so. Any runny nose? poops okay? drinks water? If sneezing stops with just water, it could be she inhaled some feed dust. Usually if something is really wrong with them you'd see discharge from the nose, hear gurgling noises, listlessness, sitting puffed up. How old? Did you get any new birds recently? If you got them all at the same time from the same place and no other birds have been around them--including wild birds, and no other people with birds have been around them, it's likely that everything is okay.