I'm going to be honest here. A VAST majority of reptile related problems can be fixed at home without a vet, and in fact in my opinion are better than a vet as a vet is stress which isn't needed outside of serious cases.

The first thing you need to find out is the cause of the mouth being swollen. Some retics make a nasty habit of "pushing" basically finding an area in the cage and pushing on it with their face/head in an attempt to get out/meet whatever need they are searching for. This could be attributed everything from temps, humidity, water, food, to breeding. If this is the case the remedy is very simple- fix the problem and give her time to heal up on her own. In my most recent case- I got in a new male- he's around 9-10 foot and very much in breed mode, in the process he pushed his face/jaw so bad that he had infected it/broke teeth, and tore himself up horribly.

The other cause could be as you said, a swollen tooth, this can be easily found by holding the snake by the neck and opening it's mouth and taking a look around. I recommend a nice pair of tweezers. If you do find a tooth, you can gently work it out by massaging the gum around the tooth and working it out.

Of course- with any scenario you're going to want to check the inside of the mouth for both trauma/wounds and a possible infection. Go pick yourself up a cheap bottle of chlorahexadine and dilute it with water. Spray the mouth out and any wounds/trauma to help fight off possible infection. Keep the husbandry right, and she should be back to normal in a week or so.