It’s not typical, but it shouldn’t be worrisome either. In fact, the way she uses the imaginary playmates (projecting her own fears onto the “scaredy cat,” for example) sounds very creative to me. This kind of behavior, incidentally, is more common in only children than in children with one or more siblings.
Your observation that she can distinguish between reality and fantasy is an important one, and the fact that your daughter makes the distinction herself should reassure you. One thing you can do to help keep the behavior in bounds is to insist that the imaginary playmates stay in the house. That means that they can’t go to the movies or to school, shopping, etc., so there is no need to worry about buckling them into the car seat. But in the house, I’d play along with her occasionally. Set a place at lunch for the friend. Ask your daughter to tell you her name, what she is wearing, what she likes to eat, etc. When the imaginary playmate’s food doesn’t get eaten, you have an opportunity to say laughingly, “Only real children eat; pretend children don’t. So I won’t need to fix her a sandwich next time. If we invite her to lunch again, we’ll just give her a make-believe sandwich.”
One final thing: ask her teacher if she ever talks about her imaginary friends at school. My guess is that she doesn’t. Instead, she, with no one to play with at home most of the time, has created her own group. As groups of real children become increasingly important and available to her, she will forget them.
P.S. to Laura: Be sure to read one of my articles on this site titled, “Archiving Your Children,” as I think you should try to write down some of her stories and keep them. Give her a tape recorder and let her tell you the stories so you can capture her own words exactly. If this doesn’t work, simply have her tell you the stories and then type them up before you forget them. And maybe she would want to draw a picture dealing with one or more of the “actors” in her little dramas. I think you will want to have a copy of some of these later, long after she has stopped playing with her imaginary friends. They will contribute more to a meaningful developmental history than will some of the countless photographs you are likely to take of her in the years ahead.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.