Your Iranian Fiancee needs permission from the US government to allow her to enter the USA. This is called a K1 Fiancee visa.
As the US does not operate any consular services in Iran, your Fiancee can choose to be interviewed at the US Embassy in Ankara, Turkey, or in Abu Dhabi, United Arab Emirates.
Once her petition arrives to the consulate, your Fiancee should contact the consulate to schedule her interview.
A week before her interview date she undergoes a medical exam at a consulate approved Medical clinic in the country of the consulate.
Finally she attends the visa interview at the consulate to demonstrate she is of good moral character and the engagement is Bona fide.
A week later she can pick up her visa, and then she can join you in the USA.
By Fred Wahl
Your Personal Immigration Guide