[windeguy]

As the other responses have indicated, it is practically impossible to bring a girlfriend (or a boyfriend) a visitor's visa to the US. Some things to know:

-You as a US Citizen cannot sponsor them for a visitor's visa. It is all on her to prove that she will return to the DR after the visa period is over. This will be extremely hard for her to do.
-Your being a boyfriend will be a big negative during the interview.
-Any other friends or relatives in the US already will be a big negative during the interview.

The reason for this is simple. A huge percentage of Dominicans have previously entered the US on visitor's visas and did not leave. This makes the interviewing officers very reluctant to grant visitor's visas to Dominicans. That said if you wish to donate $130 to the US government, feel free to do so. Hundreds of people do that daily when they pay for the visa application fee only to get a NO answer.