When I was about that age, I was very much like your daughter (the first born, had a younger sister 3 years behind me, very outgoing, very intelligent) and I had an imaginary friend named Foxy. He was a fox (very original name, I know!) who walked upright and was about as tall as I was. I can still picture him to this day. He was so cute! :-) I think I created him after watching "The Fox and the Hound". Anyhoo, I would tell my mom what Foxy and I did that day, that Foxy liked the lunch she made, etc. and she would just smile and said something like, "That sounds like fun," or "That's nice of him." She didn't ever show any concern about it, especially since I had friends and did other socializing things with real people. I personally (this is just my own theory, based solely on my experience) think kids create imaginary friends as a way to counteract the limitations of human relationships. Your imaginary friend always likes you, always wants to play what you want to play, is always nice to you, is always available...basically it's a realtionship where the child gets whatever they want. Imaginary friends are comforting and fun to their kid. I know if I had a fight with one of my friends or I was mad at my mom or annoyed with my baby sister or just plain bored, Foxy would always want to play with me, whatever I wanted, and the other person was always wrong. Kids that age are really starting to understand the limitations and imperfections of human beings, and I think imaginary friends give kids an outlet where they are in control and everything is harmonious in their world. It helps them sort out their frustrations when people, other kids, or life in general let them down. Kind of like a diary might be for an older child. After playing with Foxy for a little while, I usually wasn't mad or bored anymore. As long as your daughter isn't using her imaginary friend to replace human relationships, let her enjoy Eddalee's company. Don't overindulge it (i.e. I wouldn't say, "It's time for dinner, go get Eddalee") but when Eddalee inevitably makes an appearance, go with it (i.e. when "Eddalee" likes your mashed potatoes, say thank you). She'll outgrow it, probably in a year or two, when she becomes better equipped to deal with life's disappointments. But when she's my age she will probably fondly remember Eddalee. I know I do, and I assure you, I am a completely well adjusted individual! And even though you can't see her, I guarantee your daughter can "see" Eddalee...Eddalee looks like whatever your daughter created in her imagination. Imaginary friends are normal, common, and I think actually a pretty sophisticated manner of a child's emotional and creative development. I hope this helps!
M.