Hi Kirsten, I can hear your pain! I too have a bossy child. She is 9 now and looking back, she's been bossy since about 4 years old. I wasnt' aware of it until year one when two friends said to thier mum they didn't want to play at our house.
Unfortunately I don't have any straightforward advice. DD is still bossy and basically I dont' let her have friends over as she seems to be alot more bossy at our place. I have also had to let her learn herself. She has never had a "best" friend and seems to change friends like underwear. It's upsetting but I really have tried everything and that's just the way she is. It's extremely sad as she's a lovely child, but she just can't help telling people what to do. I guess she learns from her parents!
Strategies we are using at the moment is affirmations: I am kind and confident. We also talk about how it feels when we have people bossing us.
To be totally honest, I don't really know what to do, I've seen counsellors, talked to people etc. It really involves changing her whole attitude which is very hard. It starts with me I know and that is the hard part. I am a control freak, but being an adult I am also able to use only when necessary (family). Children can't differentiate.
Im sorry Im not much more help, I will look forward to other answers xox