Imaginary friends can be fun, but can also help kids work stuff out if they are worried about something, because they can talk it through with their 'friend', or let you know their 'friend' is worried about something.

A friend's little girl has a number of imaginary friends, 'big sister', sheep, husband. 'Big sister' came along when her mum was pregnant and she was working out all the things that big sisters have to do for their siblings.

We live in fire affected area, and they were evacuated whilst the little girls dad is a firefighter. A couple weeks later (when they were back home and everything ok), her imaginary husband (who has same name as her Dad) was burnt to death in the fires. Even though she hadn't seemed worried about the fires, her role play showed that she was obviously aware of it, she knew that people had died in the fires and it was playing on her mind. I don't think it was freaking her out, this was just her way of working out all the thoughts in her head.

I don't know if i have reassured you or not. Sometimes her imaginary friend is just for play, but other times helps her make sense of the world.