How are all of the housing stats? Heat, humidity, etc.. Did you check the mouth for redness, paleness, puss? Any unusually sounds she's making? Had she recently stuck and missed a rat or hit the side of the enclosure?

If there are no signs of illness and the housing is perfect I'd give it a couple days to see if the swelling gets better. If it does not you'll need to see a vet.

My retic ended up damaging a tooth by hitting the side wall of her enclosure while striking at her food one day. It basically caused an accessed tooth that would flare up and cause her lip to swell after almost every feeding. She was treated with antibiotics on two separate occasions, multiple treatments each time at the vet, but the actual problem didn't completely go away until that tooth worked its way out many months later.

These things are always a possibility. Especially with the species that have 2 rows of teeth and hit so hard when they strike.

So like I said, check everything out very well. If it does not look right, is red, or pale white, or has red speckles, take her to the vet for infection. Check all the tissue in the mouth and be sure the trachea isn't swelling. If it looks normal except for that one irritated spot, watch it for a couple days for improvement.