Good grief, I haven’t seen that series in years. About the only thing I clearly remember is that the end of the 2nd movie and the beginning of the third are supposed to be happening within seconds of each other. There was a three year gap in making them, so the one girl (played by Patty Dunning according to Wiki) is obviously several years older in the third. I can’t find her age, but she must have been early-mid teens to have changed that much.
It’s the story of the 7 year tribulation on earth after the rapture. In that school of theology, the rapture happens and then there’s still a lot of stuff to come.
OK, pull up a chair & welcome to a crash course on Rapturism, ca. 1830-
In this view, the Rapture differs from the Return of Christ. Jesus only comes back far enough to raise all Christians off into Heaven. Over the next seven years- “The Tribulation”, the AntiChrist rises into power to the acclaim of much of humanity. However, many others, including Jews (144,000 at first, then the majority of them), now accept Christ, and are persecuted by AntiChrist. God releases plagues against the AntiChrist’s society. Christ & the Raptured Christians finally return to Earth to defeat AntiChrist at Armageddon, raise up the Tribulation martyrs, rescue the living Christians & establish Jesus’s Thousand-Year Kingdom, which will seque into Eternity.
Or what AntinorO1 said. 
Patty was the girl from the 1st & 2nd. You’re thinking of Sandy.
OMG!!! THEY ARE TRYING TO LAUNCH PRODUCTION ON THE FIFTH IN THE SERIES!
http://www.battleofarmageddonfilm.com/battle-of-armageddon-synopsis.php
We know what has to be done. After all, it’s the only way to be sure.
Ah, it was Sandy. Got my names mixed up. Like I said, haven’t seen them in something like 15 years.
Here’s how the rapture is supposed to go down, according to popular fundamentalism beliefs:
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Everyone is milling about on earth, minding their own business, and watching American Idol or some shit.
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The dead will rise first. Yeh, christian zombies. But have no fear, they’re not hanging around long… yet.
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In the blink of an eye, the living faithful will be warp-drived to God knows where. Probably leaving behind their clothes, fillings, and hip replacements.
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This brings on the seven year Tribulation, where the anti-christ (scott biao?!) is supposed to come into power and bring the nations together, with his right hand man, Mr. False Prophet. During this time, those raptured are just gone, and there’s peace love and happiness for 3.5 years before the shit hits the fan. Then 3.5 years of the mark of the beast, 666 and some form of totalitarianism. Wormwood falls outta the sky, and poisons the waters, offing 1/3 of the remaining population, and IIRC, sending another 1/3 of the population in extreme agony… wishing they were dead. Or something. Bad stuff.
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It’s been 7 years since the rapture, bring the tribulation to an end. And lo, Jesus comes flying out of heaven on a mean-ass looking horse, pimped out in full-on Revelation gear, with a flaming sword. Behind him is all the christian zombies, in new bodies not unlike that of Jesus’ after his reassertion. Thus starts…
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You guessed it, Armageddon. Ahh the big battle between Satan, his minions and the rest of the population of earth. Truly a site to see, putting Michael Bay to shame.
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We, of course know who wins, so no big surprise there.
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Satan is now locked in a volcano with his buddy Xenu for 1000 years, along with the rest of the damned.
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This brings on a New age. The Third Millennium, and that of a new earth, restored to its pre-Adamite glory, where all the christian zombies will live in euphoria for the next 1000 years.
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After this point, is where it gets kind of fuzzy for me. I think Satan is then allowed to infiltrate this new earth, and get one last chance at corruption and duping the reborn. Not sure why God would do that, but who am I to question? Xenu, during this, is probably taking a nap.
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Then, Eternity. This is where the bible loses its scope, and even the far right end-time nuts are hard pressed to come up with anything.
It’s been a while, but this is how I remember it being taught, but in a not so quite entertaining, blockbuster-style tone. No, it was more of someone trying to scare the ever-living shit out of an 11 year old boy.
So you have hell on earth and Jebus massing his army, what happens to the 1/3 who get offed? Do they become Christian Zombies? Get stuck in a waiting room? Hit the showers?
Damn if I can remember. Maybe get recruited into Satan’s army? All I know is, if you missed the rapture boat the first time around, you’re skeee-rewed.
No, Bill Gates.
Well, somebody needs to sit these Rapture folks down and explain to them that if they’re going to go with that plotline, it’s seriously going to limit the merchandising possibilites. I think we need to get them, Michael Bay, Jerry Bruckheimer, and Roland Emmerlich together for a strategy meeting. Once these Rapturists realize how much money they can make from merchandizing, they’ll want to drop that silly storyline and go with something more conventional. Like giant slugs or something.
I’m thinkin’ Ewoks.
Satan’s little shock troops. Awwwww, cuuuuuuute! 
While it’s certainly possible that Christians get killed in the various plagues & disasters (collateral damage), the fact that the disasters are in areas dominated by the AntiChrist indicates that most killed are probably happy citizens of the Beast system and therefore go to Hell.
That is, according to this interpretation.
Seems to me that if the Christians want to be rescued from those areas, all they have to do is offee up their virgin daughters. After all, it worked for Lot.