I am sorry to hear you are worried about your dog. I am a veterinarian and will do my best to help.
How long ago did this happen, how long has she had trouble with her leg now?
This could be due to many things. She could have gotten a beesting or insect or spider bite. She could have some problem in her lower spine affecting the use of that leg, like a slipped disc, pinched nerve, or an FCE, or fibrocartilagenous embolism which is a piece of cartilage lodged in the spine that happens very suddenly.
It is a good sign she is licking
the leg. That means she can feel it, and that means she still has nerve feeling in the area.
I really would need to see and examine her to tell you which of these she might have. I hope it is a bite or sting, since that will get better with some time.
You could try a little aspirin if she is eating and not vomiting. The dose is a baby or low dose aspirin per 15 to 20 pounds of body weight, with food. If you decide to have your veterinarian look at her, he or she would have better prescription medication for pain and inflammation.
Let me know what else I can help with or answer and how she is doing.