As with so much in Biblical studies, I think that you can find much to support as well as to challenge the role Magdalene had as a preacher of Christ's word. I think that there is much out there in Biblical scholarship to indicate that Magdalene occupied a central role in spreading the word of Christ. This is enhanced by the notion that Magdalene was present at his crucifixion. Some argue that Christ rose from the dead to tell the women, specifically Mary, to spread the word of his resurrection. Harvard theologian Karen King argues similarly in this intense role of Magdalene in the spreading of Christ's belief system and set of core values:
King cites references in the Gospel of John that the risen Jesus gives Mary special teaching and commissions her as an 'Apostle to the Apostles.' Mary is the first to announce the resurrection and to fulfill the role of an Apostle─someone sent by Jesus with a special message or commission, to spread the gospel ('good news') and to lead the early church.
This is enhanced by the idea that Mary Magdalene is amongst the first to notify the other apostles, who fled from Christ's crucifixion, of his rising from the dead and the resurrection of the savior. Mary Magdalene's role as "Apostle to the Apostles" would include significant preaching because of her compulsion and her close emotional and spiritual proximity to Christ, himself. In the end, this becomes one of the central tenets to her role as a preacher and believer in the word of Jesus.