Getting married

I plan on marrying my girlfriend that is from Santo Domingo. With me being an American citizen, would that expedite her approval to get a visa much quicker to come back to the U.S. with me permanantely?

While it will help you still need to go through the process. You will need to show its a real relationship.  How long have you known her? How did you meet? How many times have you been back to visit? How.much do you know about each other etc etc

Think twice pal, and have a long betrothal............like 5 or more years.