Registered marriage validity?

One of my friends married right as she stepped into leggally marriagable age, under the special marriage act. She did that as she was emotionally black mailed by her boy friend who belongs to a different religion and economic status. Now after many years, she was well settled in life. But she continued obliging to her legal husband becuase of mental torture because of the fact that she had nobody else to confide in. Her parents arranged her marriage with someone of their liking. The marriage took place according to hindu customs and was registered. Which of the two marriages are now valid? How can she nullify the first marriage which she did in unfit mental state?