You will not know what it is until you take her to the vet.
I would not give her medication for the pain, because then she will not feel it and walk/run on it and probably make the injury worse.
Could be a sprain, could be a ligament injury, could be a number of things.
I have no idea what Juno might have, but I can tell you what it was when Hans was limping. It was a shoulder muscle strain. What I did was keep him in his crate for a few days and not let him do much at all.