Don't panic!
We use salts for various ailments but they aren't always effective on their own so for the moment, don't worry about the salt.
A few quick questions for you:
How long has the tank been set up?
What is your nitrate, ammonia and nitrite reading?
How long has the fish been sick--days, hours,--a week?
How long have you had this particular fish?
How many and what other species in the 55 with her?
What have you done so far for the nitrate?
In the meantime do this:
30% partial water change using a good quality dechlorinator. Siphon the gravel
Add Epsom salt at the rate of 1 tablespoon per 5gallons--dissolve it first and add it gradually over 6-8 hours time.
Robin