So today I let my girls out and about 1hr later I noticed that one was kinda laying around. When she got up to walk she was limping. A little later she would limp, then sit down, she flew to the run, then set down. I picked her up and looked at the legs, and she was holding the one tight up against her. I was able to pull the other leg down, but not the one she was limping on. She's about 4yrs. Old. What could be going on? Please help me? Thank you