What Could Red Raised Bumps On Inner Arm Suggest?

Hi.,My granddaughter is 8. she developed at red raised bump on her inner arm,in the bends of the arm,a wk ago. it was itchy.yesterday my daughter took her to the drs. where they talked about mercer???and gave an anibotic, which he never sent off to CVS here in westbrook,Me.Since they pushed into the main artery,she fainted on the table, but came right back. this morning it hurt,so off to the ER at MMC,our Big hospital in Portland, Me.What do you think it is. to ease my mind.They circled the bump,incase it got bigger. she is a fair/redhead also. A concerned nana..Shelley