Some people may disagree, but if my horse has a swollen leg, I tend to just treat it myself at home. Don't get me wrong, I don't put my horse's wellbeing at risk, I just don't think its necessary to call the vet for a swollen leg that was probably caused by a minor injury. I don't think that there's much the vet can do anyway. Plus, calling the vet is going to cause your horse serious distress, Its probably not in her best interest unless she's clearly in pain or suffering.
The treatmet you can provide her is much the same as if it was your own leg. If you had the same problem with your own leg, you'duse RICE treatment (rest, ice, compression, elevation). Do the same with your horse (not elevation though lol) and I'm sure she'll get better. However, if its not getting better within a reasonable time period, I'd definitely ring the vet.
Or, if she's currently very lame and not bearing weight on the leg or your very worried, I'd call the vet. But the information you've given, I'd just wait and let nature do the healing if your horse isn't suffering.
When I bestride him, I soar, I am a hawk: he trots the air; the earth sings when he touches it; the basest horn of his hoof is more musical than the pipe of Hermes. ~William Shakespeare