In a lighter vein, do watch some latest Tamil or Hindi movie, where this has happened, engage some goondas. smuggle that girl and get married!!
Now, to the serious questions. Irrespective of whatever be the pressures, no one, can legally stop you from getting married to this girl.
However, you also can take the help of good advocate and go to the court, pleading that they produce the girl in court. This cannot be avoided, since you can always point out that her life is in danger. Once done, in the presence of so many people in the court, if the girl gives it in writing or even orally declares that she is a major and has every right to get married to you, chances are that the court will take your submission and the girl's submission on record, and order the concerned authorities and relatives, including the police, to release the girl.
The next step is to bring in all your relatives, in say, hundreds, and get her married to her, in a register marriage. Once this is done, you can have a normal marriage, with all relatives and friends attending it.
There are also chances that since the court will be so serious, the girl's parents and relatives will also start seeing reason and unite both of you, though this is just a possibility.
Taking judicial help is the only sane way out in this situation. Of course, you can also approach human rights specialists who can also guide you.