Alright, so I poked the swelling with a needle and tried to aspirate fluid. I poked two different places (used two different needles). I wasn't able to extract any fluid using the syringe. Then I tried to work fluid out of the swelling using a cloth. One of the holes bled some and produced some clear fluid, but not much. The other produced no fluid at all... not even blood.
So, so much for the swelling being full of pus.
I did go to the feed store, and the only antibiotics they had were duramycin, injectable tetracycline, and penicillin. I bought the tretracycline (I know, she's already had it through the drinking water). I figured maybe I would have more luck with an injection. Well, two days of .25cc of 200mg has not reduced the swelling. No respiratory distress. Eating and drinking fine. I think it MAY have gone down a bit since last night, so I'm going to do the wait and see approach for a few days unless she gets worse.