Imaginary friend going home

So last night I was walking around with Laura trying to get her to go to sleep when she says to me, I think I'm really mad. I ask her why, and she replies, "because I don't want Annie to leave". (Annie being an imaginary friend we've had around here lately.) So I say, "well it's ok if Annie spends the night...she can stay." To which Laura says, "no, she has to go, she has work to do" At which point Laura again gets upset b/c she wants Annie to stay. Eventually after a few minutes of both Chris and I trying to reason with a 3 year olds imagination we worked it out that Annie should indeed go home for the night, but that she (or if she was still busy a different imaginary friend) could come back over tomorrow.