I'm not sure if Ariel's friend was in the episode "A penny for your thoughts" (I think that's the name of it) but the actress who played the possessed little girl is actually Kay Panabaker. The only reason I know is because it bothered me that she looked so familiar when I saw it. Turns out her older sister played on SVU a few weeks before. And Ariel's friend is played by Holliston Coleman, another actress I recognized from SVU. I think I know too much for my own good...