My cousin just starting going to a Mormon church. She once used to go to a christian church but has started going to church with her ex-mother-in-law. How should I begin to tell that the church she is going is not one of Christ and is pretty much a cult? Any help would be greatly appreciated.
Though Mormonism started in a cult-like fashion (people following a charismatic leader), it did not remain a cult. Cults fade or abruptly end when the charismatic leader dies. Mormonism survived that transition point, though it began to splinter at that point. So calling it a cult is not accurate, nor will it help you make progress with your cousin.
Mormonism is based on feelings or emotions, very much like charismatic and Pentecostal groups. Logic and facts plays little part in the decision to become a Mormon. Rather, a person is urged to pray to the Holy Spirit and find it in their hearts whether the things taught are true or not. In other words, they are being asked to decide truth based on their own personal feelings. And when it comes to feelings, my feelings are just as good as your feelings, so on that level there is no persuasion of truth.
Thus we must approach it from a level Mormonism cannot reach. "For though we walk in the flesh, we don't wage war according to the flesh; for the weapons of our warfare are not of the flesh, but mighty before God to the throwing down of strongholds, throwing down imaginations and every high thing that is exalted against the knowledge of God, and bringing every thought into captivity to the obedience of Christ" (II Corinthians 10:3-5). The answer is by contrasting Mormonism with what the Bible teaches. Mormons accept the Bible, at least in part. They are told that it is true, but it has been corrupted over the years. If your cousin is willing to accept the Bible as truth, then start studying it with her. Point out the many ways Mormon teaching differs from the Bible. There are numerous articles and sermon outlines which will help you in your discussions. Keep the discussions civil and to the facts. She will either be interested or she will dismiss the arguments. Either way, know that you have done the best that you could in warning her, but ultimately the choice will be hers to make.