Ariel Courtland told WOOD radio, Grand Rapids, Mich., she will marry Sean Phillips, who was convicted in April of unlawful imprisonment of his daughter with Courtland, Katherine Phillips, who has not been seen since disappearing from her Ludington, Mich., home June 29, 2011.
Courtland told WOOD Tuesday she hopes marrying Sean Phillips will enable her to get close enough to him to ask questions about their daughter.
She cannot visit him in prison because she is not immediate family and she is a victim in the case, ABC News reported.
"I need to have answers," Courtland told WOOD Tuesday. "I've taken all the steps to try to avoid this."
WOOD posted on its website what it said was a letter Sean Phillips wrote from prison, in which he appeared to provide details about his daughter's death.
Courtland's mother, April Lange, told the news station the letter shows Courtland was not responsible for the disappearance of Katherine Phillips.
Shortly after Sean Phillips was sentenced to 10-to-15 years in prison, prosecutors said the disappearance was being investigated as a homicide.
During Sean Philips' trial, Courtland testified she had discussed with him giving Katherine up for adoption but said she eventually decided against that.