We are planning to move states about 3 weeks before DDs birthday.
It is wrong to organise and have a party a month before with her friends?
My concern otherwise is that she won't really have a party at our new destination. But a month before seems a bit early. But any later and most of the house will be packed. Although one option could be to have it somewhere like a playground (indoor or outdoor).
There are no hard & fast rules about when you must throw a birthday party. I know plenty of people whose kids have birthdays during school holidays, and they host parties during totally different times of the year.
I think it's a great idea and a nice way for her to say goodbye to her friends. I was in a similar situation with moving interstate just after my DD turned 5. We had a gorgeous fairy party with her school friends and the photos are sentimental now as she hasn't seen any of them since.
Good luck with it and all the best with the big move.