The only "evidence" is some unreliable eyewitness accounts of sightings happening months to years after her disappearance and some questionable analysis of online photos. I found none of it credible or interesting at all.
At 5:30 am she was seen on the balcony of her family's room. Nothing happened to wake up a room full of sleeping people between 5:30 - 6 am, at which point she was noticed missing.
So the kidnap theory is that she left the room of her own accord barefoot in a t-shirt and jeans sometime between 5:30- 6 am, and her kidnappers saw that she had left her room, were able to snag her from a public area of the ship without notice, and then smuggle her unnoticed off of the ship in Curacao. Oh, and the ringleader of this kidnapping effort was the bass player of the ship's band... and the entire ship's crew was in on identifying and assisting with the abduction of young women for Caribbean sex-trafficking.