You can claim your girlfriend as a dependent if you meet the following requirements:
She lived with you for the entire year.
She did not earn more than 4,050 dollars during the year.
You provided more than half of her support.
If she is only claimed as your dependent, the government cannot levy your refund to pay for her child support liabilities. However, if you get married and file a joint income tax return, the government could levy your refund because she would be a signing party on your return (Don’t worry, there is a fix for this issue if you do get married :))