I am a confessional Lutheran (LCMS) and do not believe in "the rapture". However, I know a bit about the millenialist concepts.
Pre-millenialism is what I assume your grandmother is; it is the teaching that has broken into pop-Christianity in America. (By that I simply mean the popular mainstream teachings of our culture.) It basically teaches that there will be a rapture where either the Strong Christians are caught up in the air at Christ's return, leaving the weaker Christians and pagans behind OR that all Christians will be caught up with Christ leaving only unbelievers behind. After the rapture will follow a tribulation (usually seven years) at which time the anti-Christ will reign on Earth and many tragedies and disasters will take place, culminating with the final return of Christ and a literal 1,000 year reign on Earth. This teaching is also closely associated with theology on Israel's political state concerning the end times.
Post-millenialism is a teaching that has largely died out, though it was popular in the middle of the 20th century. This theology (also popular among protestants in its time) professed that we were working toward a 1,000 year reign on Earth. Basically that God was going to continue to sanctify His Church and the world until it was in a state "worthy" of God's political rule over it. This was driven by the soft-eugenics of the time and the belief that the advances in science and medicine were going to solve all the world's problems, and also the ideology that WWI was the "war to end all wars". Obviously, none of that came to pass and the theology fell out of mainstream.
The longstanding stance of Christianity from ancient times has not fallen into either of these categories. The majority of Christians over the ages have been in agreement that this is not how Scripture is to be interpreted on this issue. The Bible does talk of Believers being "caught up in the air" to be with Christ when He comes again. Although this literally could be called a rapture, it is not an event that precedes a tribulation or some other political reign on Earth. This can be thought of as the first event in a series of events IMMEDIATELY FOLLOWING that culminate in the destruction of God's enemies, the glorification of God's people and the creation of a new heaven and a new Earth.
Is there to be a tribulation in the end times? Yes, but the tribulation precedes the rapture, not the other way around. A proper interpretation of Revelation and the Bible will reveal that we are now in the End Times and have been since the first Pentecost recorded in the book of Acts. Indeed ever since Christ's resurrection we have been in the Last Days and the End Times. We are now in the tribulation.
Although the Anti-Christ may be personified more in one particular person, organization or office, really the spirit of Anti-Christ has been around ever since the beginning of the end times, that is for thousands of years now. This "spirit" of Anti-Christ really just means any one or anything that claims to be Christ or speak for Him in any way that Christ Himself has not commanded. The confessions of the Lutheran Church teach that the Antichrist spoken of in Scripture is personified most clearly in the office of the Pope. Although many Lutherans do not hold steadfastly to this teaching, there is a good amount of contextual Biblical evidence in Revelation and historical evidence to back up this claim.
The Christian Church unanimously confesses that there will be a literal resurrection of the dead at Christ's return, and this will include all people, believers and unbelievers alike.
Two of the most severe problems I see with the contemporary view of the rapture and the end times are these:
1. With the focus on a political kingdom and the state of the country of Israel in heralding Christ's return, there is some belief that there will be some separate plan of salvation for the Jewish people as they were God's chosen race. However, Scripture clearly teaches that Jesus is the only way for salvation and there is no other. The new Israel is not a political state but is the Church; believers in Christ are to receive Israel's inheritance. A different "path of salvation" for unbelieving Jews goes directly against the Christian teaching that Jesus is the only Way.
2. For those who believe that only an elite level of Christians will be taken up in the rapture, this is dangerous because it causes division in the Church where there should not be any. It causes fear and confusion rather than providing comfort in salvation, and it causes us to focus inward on ourselves and our own works rather than focusing on Christ and His perfect life, death and resurrection. Jesus is the center of the faith and the contemporary views of the End Times that are now popular take Christ and His saving work out of the center, which is a dangerous precedent.
(Sorry, not sure how do embedded links in this new format.)
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