Van Diest, 18, went missing in 2011, after leaving home in the early evening to meet a friend. She was found badly beaten by the side of railroad tracks, and died later in hospital.
Matthew Foerster, 28, of Cherryville, was found guilty of her murder in April. His 60-year-old father Stephen is now on trial for obstruction of justice and accessory after the fact. Prosecutors have indicated Stephen is expected to plead guilty to the charges today.
Van Diest's mother Marie says she'll be in court for Stephen Foerster's appearance Wednesday.
"We're interested in seeing justice done. It's something we feel we need to do. Just hearing about it isn't quite the same. We need to be there up close and personal."
Three years ago, Van Diest had left home at around 6 p.m. to meet a friend.
She had been walking along the tracks, dressed like a zombie for Halloween, and was texting back and forth with her friend.
In the last text her friend received, Van Diest wrote about "being creeped," meaning followed.
Police later identified Matthew Foerster and his father Stephen as suspects.
During Matthew Foerster's murder trial, a forensic pathologist testified that Van Diest died from one or more fatal blows to her head.
Foerster admitted in court, through his lawyer, to causing her injuries, and Crown counsel argued that Foerster caused those wounds while trying to sexually assault her.
His guilty conviction of first-degree murder means he faces life in prison with no eligibility for parole for 25 years.