My dog got stung by something on her nose and the area is hard and went bald .what do I do

How long ago did you first notice this issue?

Was this a recent sting? Or did it happen hours or days ago?
If not recent and she has shown no signs of allergic reaction such as swelling or difficulty breathing, then you may be seeing the bodies natural reaction to the sting. If recent then you may to consult a Vet to ensure that there is no reaction.