It is hard to know for sure that she has salpingitis—you can only notice her symptoms. If antibiotics are used early, then those might help, but there is an egg withdrawal time, and many people prefer not to give antibiotics. If you use one, amoxicllin or enrofloxacin are used. Amoxicillin is impossible to get without a prescription at this time, unless you have some put away. Enrofloxacin or Baytril is found online from Jedds.com. It is banned for chickens because the FDA worries about antibiotic resistance of campylobacter, a common bacteria we can get from handling chickens or eating undercooked chicken. If that doesn’t bother you, the 10% liquid dosage is 0.25 ml twice a day for 5 days. But without having a diagnosis, I might watch her.
I tend to leave all hens in the coop with the others to maintain the current pecking order. Is she being roughed up or bullied? If that is a problem, I would keep her in the coop and run inside a dog crate with food and water. If the coop is too small, maybe just bring her out in the mornings to spend the day.