I gave her time—Jesus, in the past, already warned the false
prophet, the leader of the sect, to stop the false teaching, but the teacher
didn’t listen to Jesus, so Jesus is going to punish her.
Throw her to a couch—The prophet and (her) group of
followers will be made seriously sick until they repent. This is a common thing for God to do against
those in serious sin (see Psalm 32)
Repent of their deeds—Jesus wants them to stop their
actions.
I will kill her children—Some of the followers will die of
the sickness.
Perhaps this seems severe on Jesus' part. Okay, it absolutely seems severe on Jesus' part. But we need to see the circumstance from Jesus' perspective.
What this sect is doing is forsaking the kingdom of Jesus, the only way that one might obtain eternal life. Not only are they forsaking this way of life, but they are giving strength to the enemy that persecutes the way of life. In the long run, Jezebel is killing people, in the most permanent way possible. Jesus has given her a chance to stop killing people, but she refuses. Jesus isn't taking any more chances that she might kill more people in his kingdom. He is taking serious action-- making her and her followers sick and some of them will die. This will show them all the seriousness of her sin.
Interestingly enough, the original Jezebel also killed people when it served her purposes.