What?! Since when was she not a prostitute that later changed her life?
Since the beginning.
She was mislabeled as a prostitute most prominently in 591 by Pope Gregory.
The Catholic Church officially corrected Pope Gregory's mistake in 1969.
Matthew 27.51-61 does not say she's a prostitute
Mark 15.35-45 does not say she's a prostitute
Mark 16.4-14 does not say she's a prostitute -- it says Jesus cast out "seven demons" from her. Demons ≠ Prostitutes. E.g.:
Mark 18-20: 18 As he was getting into the boat, the man who had been possessed by demons begged him that he might be with him. 19 But Jesus* refused, and said to him, ‘Go home to your friends, and tell them how much the Lord has done for you, and what mercy he has shown you.’ 20 And he went away and began to proclaim in the Decapolis how much Jesus had done for him; and everyone was amazed.
Luke 8.2 also refers to casting out demons, no mention of prostitution: "The twelve were with him, 2 as well as some women who had been cured of evil spirits and infirmities: Mary, called Magdalene, from whom seven demons had gone out, 3 and Joanna, the wife of Herod’s steward Chuza, and Susanna, and many others, who provided for them* out of their resources."
The source of this slander is in Luke 7 36-50. In that passage, an unnamed woman anoints Jesus' feet. A Pharisee says "Jesus can't be a prophet, he let this sinner touch him." Jesus then reads the Pharisee the riot act, saying "she treated me with hospitality, you didn't; so her sins are forgiven, but yours are not." Jesus then says to the woman: "Your faith has saved you; go in peace." The unnamed woman isn't called Mary, isn't called Magdalene, and doesn't join his entourage.
Mary Magdalene wasn't a prostitute, not ever. She was a disciple. It's amazing how long errors like this can persist.