I take it your "girl friend" is someone you have never met yet in person but who picked you up on a dating or social networking site and has convinced you that the two of you will live happily ever after.
Why do I say that? Because this basic travel requirement is a standard lie found in internet romance frauds. The US doesn't require someone to have all of that money to visit here, and Turkey doesn't require money to leave it.
The US government warns Americans to avoid internet romance schemes and to walk away from anyone who asks you for money for a Travel allowance. There's just no such thing. The US State Department
"Beware of anyone who requests funds for a BTA, or Basic Travel Allowance, as a requirement to depart another country for the United States. There is no such thing as a BTA.
In other cases, your Internet friend will claim to need a travel allowance, or travel money, to be able to travel to the United States. Again, there is no such requirement under U.S. law"
This woman is a scammer. She has asked you for the one thing that proves conclusively that she is a fraud.
Walk away from her so she doesn't manipulate you any further. Don't empower her further. Just seek all contact. If you've already sent her money, report the fraud to your police and to the FBI at IC3.gov.