Def by Temptation

The story is set in New York and revolves around the relationship between two childhood best friends: "Joel", who is raised by his religious grandmother after both of his parents are killed in an automobile accident, and "K" who abandons religion, moves to New York and becomes a movie star. Joel (now a minister like his deceased father), becomes somewhat disillusioned with Christianity and decides to take a trip to New York to visit his friend, K. While awaiting Joel's arrival, K (played by Kadeem Hardison) visits the local bar and meets the perfect woman (played by Cynthia Bond)--who in reality is a succubus seeking blood, and vengeance against any and all men foolish enough to be tempted by her.
The audience is first given a taste of the demon's powers when shortly before meeting K, she seduces and then kills an employee of the local bar she uses as her hunting ground. Later, during sexual intercourse with a patron of the bar (a closeted homosexual), she transforms into a beast and kills him, horribly. During another seduction (and after having met K) she infects a married man with an incurable, flesh-eating disease before sending him home to his wife who promptly shoots him. Later, when K attempts to introduce her to Joel (played by James Bond III) he is astonished when she pretends to have never met him and spends the entire evening with Joel. It is then that K meets fellow bar patron "Dougy" an unsuccessful pickup artist (played by Bill Nunn). The next day when she calls on Joel at K's apartment, K decides to confront her and notices that she casts no reflection in the mirror. A frightened K stands passively by as she and Joel leave on a date. K heads to the bar hoping to find Dougy. After confiding in Dougy the day's events. Dougy reveals himself to be an undercover agent belonging to a special task force investigating a string of strange occurrences, disappearances and murders centered around the bar.
Dougy and K pay a visit to a medium--Madame Sonia (played by Melba Moore), who goes into a trance and advises them not only of the nature of the demon but also the fact that Joel has been drawn to New York and is being specifically targeted by the demon because of his ministerial bloodline. Madame Sonia then channels the demon, who becomes aware of their quest when Madame Sonia reveals its name "Temptation". Dougy and K return to the bar and attempt to exorcise "Temptation" who easily overpowers them. They escape but in doing so, fatefully decide to head off in different directions.
Dougy and K both lose their souls.
Later that night, Joel who is confused goes to "Temptation's" apartment. There the demon attempts to ply him with wine but when Joel refuses, she takes a sip and forcefully kisses him with the wine on her lips. Joel passes out but awakens at some point from nightmares to find himself in the temptress' bed. He is confronted by the phantom of his deceased minister father (played by Samuel Jackson) but when Joel realizes that the phantom is not his father, the demon appears in its true form. Alerted by K earlier that evening after the visit with Madame Sonia, Joel's grandmother suddenly bursts into the bedroom with a bible. Joel realizes what he must do and destroys the demon with a renewed sense of faith in the Word of God. Joel returns home to become a world-renowned minister.
The Plot twist at the end reveals that in the interim, Dougy has become the new "Temptation" and K, his ghoulish limousine driver. This transformation is made clear to the audience when a female at the bar lights a cigarette for Dougy with a match, Dougy is heard saying "You should use a cigarette lighter next time--The flame lasts longer" â the opening line of the female "Temptation".

Question: What does Joel's grandmother do?
Answer: She bursts into the room with a bible