Nowhere in The Bible does it say anything about a Christian who God will give the explicit power of telepathic conversion. However, it does say something about The Antichrist (or at least an antichrist) coming in the light and claiming to be Jesus (or, at least in this case, a special chosen one of His). In the midst of Vince's Bible cram session early on in the film, about 3-4 scenes or so before Sheri discovers her new power, this is actually slightly eluded to when he mentions a verse saying in basic terms that not all angels and spirits that appear are there to minister in good.
Vince is also the one that says that the Devil's main tricks are to deceive, trick, and scare you. Apparently he wasn't alert enough to this all, because anyone who's decently well-versed in even a handful of key points within the New Testament would know that God wants people to, y'know, actually choose Him, which Sheri's power completely defeats the purpose of, instead opting for the "mass-church-dependency" approach. You would think Pastor Jeff would know this, but if his reasoning that everything is going to hell and it's pissing him off before he devises his plan is any indication, he's basically allowed anger to cloud his judgment.
The fact that Old Scratch shapeshifts through the exact same bright light as the supposed "Holy Spirit" Vince and Sheri saw on the chandelier, and the fact that the Devil effectively does nothing truly sinister in this film besides mess with Sheri at such a gradually increasing pace it's like he's guiding her along to this path, should've tipped off at least Sheri at some point that something was wrong here. Instead, she continues right along using her power to produce a world that is superficially far better and more "Godly" than reality, but consists of little more than guilt-tripped androidized people who, despite her sermon in the last church scene before her death of leukemia, never get the chance to actually make their own choice as to where they stand within eternity. And since people generally have to choose Jesus to get to heaven according to anyone who knows the first thing about Christianity, the fact that they never actually get to choose means they're basically all following what they think is God's will all the way to hell.
Speaking of which, her disease itself. She shows no outward signs of any trouble or difficulty with life as a result of it. This is probably intentional, as the doctor even lampshades this in the middle of the film. Either God is truly keeping her alive to do His work as the movie claims, or it's Satan masking the disease just long enough for her to bring about this artificially-cleansed world.
Last but not least, in a film that is supposedly a straightforward Christian work, during the view of the photos on the fireplace there's a wooden pentacle with cherries hidden in the middle there. Either this was supernaturally put there without anyone really noticing it or Sheri's family bought/found it and put it there and they're all complete idiots.
Speaking of Sheri's family and the ending of the movie, that brings us to one last conclusion
- The pentagram is an ancient Christian symbol; the association with the Devil is new and unique to certain churches. It's especially common these days as a Christmas decoration.
No, not in the middle of the shapeshifting sequence where Sheri ends up calling Satan a loser. That's obvious. But rather, in the supposedly heavenly dance hall. Going from the last WMG, Satan taking the shape of mommy and crafting this dance hall for her was one last ploy of deception, one last moment of impersonating her mother, before revealing to her the entire plan and the way that he used her to turn God into Big Brother.
And for those saying that Sheri can't be in Hell because she didn't choose the Devil, her dad did tell her that she could stop this route at any time. Not only did she continue, she actually told him she didn't want to stop. As Al Pacino put it best in The Devil's Advocate, he only set the stage. She pulled her own strings.
Sheri has been deliberatly chosen and infected with the Euphoria Virus, in a movement to render the American people docile and more pliable to control.
- The Euphoria Virus, which rendered people happy and carefree, had infected the populace back in the '60s, as seen in Whats So Bad About Feeling Good?. through an infected toucan and the beatniks who protected it. At first the virus was considered harmless, as it had drastically reduced domestic abuse, road rage and public rudeness. But the Public Health sector stepped in when it was feared that such public happiness would also reduce people's willingness to work, to vote, to wage war; more importantly the tobacco, liquor and pharmacy industries objected to the fact that the affected no longer needed to buy their products. (It was the 60s, after all, everyone was expected to smoke, drink, and pop pills.)The virus was isolated, an antidote swiftly applied to the general public, and the old chaotic order was returned. But it's very likely that such a mind-altering virus would also be preserved and studied with an eye for potential use, esp as a bioweapon.
By the 21st Century it's not impossible that some might reconsider the placidity of Euphoria Virus carriers as a means to quell civil uprest. By now the virus may have been altered enough to have its victims become more susceptible to outside influence, including hypnotic suggestion (as in Sheri's vision of the cross). A few rogue officials, disgusted with the current attitude of the public toward authority, may have smuggled a few samples out of the lab it's stored in, with an eye to releasing it. This may be dovetail with the quiet intrusion of various radical Christians into politics. In particular the more extreme followers, on learning of its effects, may decide to use the virus as a means of forcing their message on people and supposedly jump-starting God's Kingdom on Earth. The abrupt massive endorphin rush released by the virus could and would be interpreted by people as the promised salvation, and encouraged by ministers, "official" Christians. In truth no-one could be certain how much was an honest conversation and how much viral brainwashing, and with the resulting docility officials would not care.
Sheri is the perfect means to spread the virus, as she is young, pretty, and dying. She had been given a massive dose of the Euphoria, disguised as treatment, by a radical Christian group who anticipated what would happen as shown in the course of the film. Of course people are impressed by her courage and hope, and in the course of meeting her, touch her, receiving the enhanced virus and in effect, being forcibly converted. The more extreme Evangelical Christian groups rally these suddenly Born-Again followers into blindly accepting all church doctrines in a major attempt to all but force "Good Christian Values" onto the American populace, ie, women staying home, abortion and homosexuality being totally illegal, automatically handing over 10% of one's money to the churches, and never ever questioning one's Christian betters.
Basically Sheri's father (and possible allies) may have secretly decided it was better to sacrifice one young girl to God's Purpose than allow the American people to go on making their own decisions, esp regarding things like sexuality.
Apparently this is no parody, and there is no hint that "Pastor" Greg Robbins or the rest of his team behind this movie even thought things through to the logical conclusion of these epileptic trees. But, that second part were never really brought to attention. It's entirely possible that this third-rate film came out this way on purpose to secretly subvert the Christian community behind a veil of preachiness meant to attract the fundamentalist crowd, repel everyone else, and send through the basic lie that God requires guiltdroids.
Leaving aside the obvious parallels with Strange Journey, The Devil does not put up very much of a fight at all - being easily thrown aside simply by calling him a loser. This is because he is meant to prop up a token resistance so as not to seem too obvious or trending towards making things suspiciously easy. That most likely is not the real Devil, being either Mastema or Satan taking on the guise of Lucifer for the purpose of the plan.
Sheri is more or less a pawn - setting the stage for the Angels to remove free will.
Fundamentally, we're seeing the start to a game before the actual protagonist shows up to deal with the mess.