(CBS/AP) PROVO, Utah - The mistress of Martin MacNeill,, is scheduled to take a much-anticipated turn on the witness stand Friday.
On Thursday, two of MacNeill's oldest daughters testified that their father was eager to demonstrate how their mother ended up dead in the tub, and how quickly he introduced a nanny who, according to the sisters, didn't cook, clean or take care of the youngest children.
The oldest sibling, Rachel MacNeill, said while growing up, her father was her best friend and that she was closer to him than to her mother. When she learned of her mother's death, she didn't suspect her father and wanted to comfort him, she said.
But her suspicions quickly grew at a family lunch after their mother's funeral, that turned sour.
Her father was "commenting on how he's a single man now, and he kept it very casual," Rachel MacNeill said. "He was making jokes about being single, and he was laughing. It made me sick. I left."
During her testimony Thursday, Rachel MacNeill was very emotional and visibly shaken as she testified against her father, reports CBS affiliate KUTV.
According to the station, Rachel testified that her father insisted the family go to a temple to pray about getting a nanny to care for the family's younger children after their mother had died.
A few days after that, MacNeill reportedly announced to the family that he hired Jillian "Gypsy" Willis as the nanny, but Rachel said she didn't look after the children or do any household chores.
"She just had eyes for my dad and wasn't doing anything a nanny would do," Rachel testified, according to the station.
Prosecutors are trying to prove that MacNeill plotted his wife's 2007 death while carrying on an affair with Willis, an aspiring nursing student. The doctor invited her to his wife's funeral, hired her as the nanny and asked her to marry him weeks later.
Willis is on probation for identity fraud charges. Prosecutor Sam Pead called her a "begrudging" witness who will confirm she had the affair and insist it's over. The two were separated by MacNeill's jailing last year.
MacNeill, 57, is accused of hounding his wife, Michele MacNeill, to have a face-lift, then mixing a lethal combination of drugs for her recovery and helping her into a bath tub.
Defense attorneys counter that she died from a heart condition. MacNeill has said he found her slumped face-down into a tub of water.
On Friday, 4th District Judge Derek Pullan is expected to decide if he'll allow the doctor's youngest daughter to testify. He is trying to determine if Ada MacNeill, now 12 years old, has her own independent memory of her mother's position when she was the first one into the bathroom.
Prosecutors expect Ada MacNeill to say she found her mother on her back in the tub, fully clothed. But defense lawyers say the girl's sisters coached her to recite that account for investigators trying to develop a theory of the death.
"We believe there has been intentional influence, and that has led to Ada's memory remarkably improving over the years, which is something generally unheard of for a child," said Randy Spencer, one of MacNeill's lawyers.