Its possible she got stung by bees, but if shes showing no sign of distress then it could be something else. Does she have plenty of shade? Dogs do get sunburned. Also check her area for poison ivy. Some dogs are alergic to poison ivy. I have a pit bull Puppy that is allergic to sun... He breaks out really bad if he gets too much sun, and our German Shepherd mix was allergic to poison ivy and had to take amoxicillin when she got into it. Good luck... Hope she feels better soon.