She if you are married in India then the divorce shall be in accordance with Indian laws since you married a american citizen kindly clearfy was it a hindu marriage or under Special marriage act.
Since you both want divorce mutual consent is best option as it will save lot of time legal fees and it will save you from lot of legal hassels.
In case she is not agreeing for mutual consent divorce you have to file a contested divorce on grounds like cruelty, adultry , desertion which ever applicable on your facts and same has to be proved before court.
There are only two options for divorce mutual or a contested divorce.