"He is not the monster the (media) would like the world to see," she writes. "He is traumatized, depressed and has an addiction. He is not a murderer."
This plea comes shortly after van der Sloot's former girlfriend spoke out about the man she described as her "first love."
Melody Granadillo says she had no indication he could be a killer, but now she feels she was lucky she wasn't hurt.
"I didn't think he was violent, but as time goes by, especially now, I think he was," said Granadillo.
Van der Sloot is now being held in Peru's notorious Castro Castro Prison in a spartan cell. Sources say the 6-foot-4-inch Dutchman is not granting interviews unless he is paid. His bed is a mattress on a slab of cement; his sink and toilet are little more than a hole in the floor.
He is being isolated from the other inmates for his own protection.
A judge is expected to interrogate the Dutchman next week about Stephany Flores' murder.
Van der Sloot has said he is ready to talk about the case, but only to Aruban authorities.
Van der Sloot's mother said in her e-mail that her son is the victim of entrapment. She is expected to come to Peru within the next few days to visit her son in prison and help him hire a new laywer.
Van der Sloot's murder trial could last as long as two years.
The Associated Press contributed to this story.