Multiple Personalities??

Over the last week Sarah has brought out different personalities. She usually insists on being called Sophia. Sophia is a baby, therefore Sarah acts like a baby. She will also call herself Mama Baby. We are not quite sure who Mama Baby is but she is usually angry and throws a lot of fits. This weekend she has been Sophia almost constantly and will get very angry if you don't call her that. She even woke up this morning and crawled into our room as Sophia. I guess this is just like having an imaginary friend except you become the friend. I also know it is common for her age to act like a baby, but Josh doesn't like this new development. I wonder how long this phase will
last?