Rosa Hill, 36, and her mother, 58-year-old Mei Li of Antioch, were convicted June 28 of first-degree murder for the death of Selma Hill at her home in the 7700 block of Peppertree Lane in Dublin in 2009.
They also were convicted of premeditated attempted murder for an attack on Rosa Hill's husband, Eric Hill, at that same location that day.
Alameda County Superior Court Judge Kenneth Burr sentenced Rosa Hill to 36 years to life in prison and Li to 25 years to life.
Prosecutor Casey Bates told jurors during the trial that Rosa Hill and Li went to Selma Hill's home, where Eric Hill and the couple's then-2-year-old daughter also lived, as part of a plot to kidnap the daughter because of a custody battle over the girl.
Rosa Hill and Eric Hill, who later divorced, were separated at the time and he had been awarded sole legal custody and 85 percent physical custody of the daughter.
Bates said Selma Hill was killed the morning of Jan. 7, 2009, and Eric Hill was wounded when Rosa Hill and her mother attacked him after he returned to the home with the couple's daughter later that day.
Bates said notes later recovered by police showed that Rosa Hill and Li called their plan "Operation Custody" and purchased a cache of weapons worthy of a small army, including guns, stun guns, a sword, a hammer tool, a crossbow, a throat cutter, a knife and a baton.
In addition, Bates said when police investigated a computer that Rosa Hill and her mother used, they discovered the two women had conducted Internet searches on how to get away with murder and how to strangle someone. They had also researched deadly substances such as arsenic, cyanide, strychnine, mustard gas and ammonia, he said.
Burr said today that the attack was "one of the most vicious, callous and premeditated crimes I've seen in my 35-year legal career."
Burr said the evidence indicated Hill and Li planned to murder Selma Hill then kidnap Eric Hill and take him to a remote location, where they would cut up his body with the tools they had in hopes it would never be found.
The judge said the evidence suggests Rosa Hill and Li planned to forge a suicide note by Eric Li in which he would admit he had killed his grandmother and had molested his daughter, a charge that Rosa Hill had levied against him during the custody battle but he had vehemently denied.
Rosa Hill then expected that the family court system would give her custody of the daughter, Burr said.
Eric Hill said today that his daughter has suffered both emotionally and physically since the attack and has night terrors, separation anxiety and fear of strangers.
He said his daughter never mentions Rosa Hill and "has a hole in her heart where her mother should be."
Eric Hill said Rosa Hill's actions "are extremely painful because she is the one I loved with all of my heart and more than anyone else."
He said the fact that she killed his grandmother and almost killed him "shakes me to the very core of my soul."
Eric Hill alas said he had trusted Li up until the time of the attack and he feels betrayed by her actions, as well.
"I find her actions extremely painful because she was my friend," Hill said.
Li and Rosa Hill didn't speak at their sentencing hearing.