Nida's Pakistani so she wouldn't have been sent to India for a marriage, I don't think. That would be unusual.
I think it may be fair to consider Nida's depression/distress may have (at least in part) been caused by pressure for an arranged marriage which are commonplace in Pakistani culture. Her family may just have chosen not to mention that factor, for personal reasons.
I also think it's possible Nida had fallen in love with someone her family did not approve of, and wished to marry him. It that had happened, it would make sense for Nida to marry quickly even though she's young, because of her immigration status. (Not suggesting she wanted a 'marriage of convenience', I'm talking about if she'd fallen in love). I think it's possible her family wouldn't reveal that either, if it was a factor.
I am wondering also, as the youngest daughter, if she was being asked to stay home and help care for her disabled father?
These could all be reasons for depressions, but it is just my speculation. I only believe there may be something else because the story of the evening Nida vanished has changed so much and still doesn't make quite add up to me.
Sadly, I think there may be another explanation; that someone did not like something Nida said or did and there has been foul play. I don't believe she is in hiding somewhere; surely even a loyal boyfriend would have told police she was safe but didn't want to go home, by now?