Women whose husbands have died are free to get remarried, but only to believers. However, they will probably be happier if they do not marry again.

1 Corinthians 7:39-40

39 Women must remain married to their husbands while their husbands are still alive. But if a woman’s husband dies, she is free to marry any unmarried man whom she wants to marry, but he must belong to the Lord. 40 However, I think that she will be happier if she does not marry again. And I believe that the Spirit of God is directing me as I say that.