Do you have other chickens? You should separate her immediately.
There are many diseases and conditions that make chickens sneeze, from allergies and reactions to dust to ammonia build-up in the coop to respiratory illnesses.
Once the chicken is separated, you can observe how much she eats, drinks, and what her poop looks like. That info may help someone with a diagnosis.
There are antibiotics, but most will not work. They have been so overused the bugs are resistant. In most cases, unless you are treating a very specific bacteria, all you end up doing is ruining their crop/digestive systems and allowing yeast or fungal infections to take over. Many of the illnesses that cause this in the first place are fungal or yeast related, so you don't want to feed the bad bugs with antibiotics.
Good luck with her.