I was looking around for something more easily accessible for you to use, and white vinegar as a topical seems like it would help. Initially it seemed like it would burn but it actually neutralizes fire ant venom.
(I found the below information on the page linked)
"Fire ants do not use formic acid in their sting, they use a cocktail of an alkaloid (a base) that is also toxic and allergenic proteins (induce an allergic effect in the body, by forcing the mass production of class E immunoglobins (IgEs). since the sting is a base, it does not make sense for ammonia or baking soda to treat a FIRE ANT sting. bases do not neutralize bases, they raise the pH. something more like white vinegar (acetic acid)or a weak acid would work(formic acid) to neutralize the sting. (Omar Fahmy)
Mentioned in the Dr's Book of Home Remedies, it kills the itch and stinging for a while, just re-apply when itching again."
You can also dose her orally with Benadryl and aspirin to decrease pain and reaction.
To dose aspirin you can cut a baby aspirin in half, which is about 40mg, or into a forth, which would be 20mg. Either is acceptable, but it depends on how comfortable you are with dosing her and how much pain you believe she's in. I wouldn't go over a half of baby aspirin. You can dissolve it in water and dropper/tube feed it to her, or mix it into a crumble or mash for her to eat.
More info here: http://www.backyardchickens.com/t/840411/using-aspirin-on-chickens
To dose benadryl you can split a benadryl tablet into a quarter and dose that, and give another quarter if it wasn't effective. More info here: http://www.backyardchickens.com/t/579161/can-you-give-a-chicken-benadryl (another poster in the thread linked also references the same article as I and recommends vinegar for fire ant stings)