There's no rule of 1yr from marriage. Fraud can be discovered at a later stage and case can be filed.
What you need is strict proof that she told you that she's bachelor prior to marriage.
Also, the date of discovery of the fraud by husband is important and should be proved. And case should be filed within one year of this discovery.
No cohabitation post discovery of the fraud.
Non disclosure of prior marriage is strong ground for annulling the marriage and there are several judgements on this. Do some research.
But on the other hand, not from legal point of view, if she's been a good wife and is apologetic about her fraud, consider accepting her. If she's aggressive, ditch her.