Last Friday My Granddaughter Woke Up Holding Her Arm. She

Last Friday my granddaughter woke up holding her arm. She did not injure it. Later after she had ibuprophen, she seemed fine. Then after a nap, she said it hurt again and was holding it stiff. I noticed some hives on her hand, but the went away within minutes. Noe she is not only saying that her arm hurts, but her knees as well. My sister had "chicken gunna" ' she said that this is how it acted. What could this be?