1. You cannot physically stop her marriage.
IOf you came to know about the exparte divorce then you may have to rush to the court to file a set aside petition to set aside the exparte divorce decision.
But the court cannot stop her marriage or nullify the remarriage if already done because it is more than one month from the date of passing the orders for exparte divorce.
What were you doing all thes one year without knowing her activities, because if at all the divorce was granted one year ago, she certainly would have filed the divorce case at least one and half a year ago, therefore it can be deemed that you were not living together for a period over two years,
Therefore it cannot be said that she had given a wrong address to obtain this divorce fraudulently since you might have changed your address in the period of separation which she may not be aware hence she had sent the summons to the address known to her, however this will not stop you from filing a set aside petition, but mere filing the set aside petition will not stop her from going ahead with her proposal to remarry until and unless there is a restrain order from court.
In that case you may have to file an application before the court along with your set aside petition seeking to restrain her from marrying again in the course of the court taking decision to set aside the exparte divorce decision.
There is no question of she committing an act of bigamy by marrying again especially when she has a divorce decree granted by a court of law.