KTLA: A stay-at-home mother of four from Orange County has been arrested on charges of killing one of her 2-year-old twins and injuring the other.

Seal Beach police say 31-year-old Linda Wilborn was arrested Monday at Orange County Social Services Agency when she visited her other three children, who were placed in protective custody last December.

She is charged with one felony count of assault on a child with force likely to produce great bodily injury resulting in death and three felony counts of child abuse, prosecutors said.

Prosecutors say Wilborn used "tremendous blunt force" on her daughter Millicent on December 17 while her husband was at work.

She then called 911 to report the toddler was not responsive, according to the Orange County District Attorney's Office.

The toddler died of a ruptured heart at a hospital and was found to have fresh and old fractures to her ribs.

Authorities say the other twin had a fractured skull.

The other two children -- a 3-year-old girl and an 8-month old boy -- did not exhibit any physical signs of trauma, according to Deputy District Attorney Scott Simmons.

Authorities do not know the motive behind the alleged murder.

Wilborn is being held on $1 million bail.

She is set to be arraigned Wednesday.

If convicted, Wilborn faces a maximum sentence of 25 years to life in prison.

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