Is it right to marry a non-Christian girl if she is willing to convert? And can we marry a girl who is divorced?
It is not wrong for a Christian to be married to a non-Christian. "For the unbelieving husband is sanctified by the wife, and the unbelieving wife is sanctified by the husband; otherwise your children would be unclean, but now they are holy" (I Corinthians 7:14). But this is only a part of what you should consider.
A person who is willing to convert to Christianity in order to marry a Christian will not really become a Christian. This person is dedicated to other person, not to the Lord. If the marriage fell through and never happened, would she still be a Christian? I very much doubt it. Would a woman make a good wife if she is willing to sell her "faith" to the highest bidder?
So while a Christian may marry a non-Christian, it might not be the wisest choice available.
If a person is divorced for any reason other than that their spouse had been sexually immoral, then if they marry another person they are guilty of adultery. The person who marries such a person is also guilty of adultery. "And I say to you, whoever divorces his wife, except for sexual immorality, and marries another, commits adultery; and whoever marries her who is divorced commits adultery" (Matthew 5:32).
If a woman divorced her spouse because he had committed fornication, then she is free to remarry and the person she marries is not sinning in marrying her.