Christine Longridge's son, Michael, caught her in the act of fatally stabbing her daughter, Rachael, Edmonton police sources allege.

Michael Longridge, 18, came home and grabbed his mother while she was stabbing Rachael, 21, at the family's Sherbrooke bungalow in Edmonton on the afternoon of Dec. 23, police sources told CBC Wednesday.

Rachael Longridge died of her injuries at the scene.

She had recently graduated at the top of her nursing class and was about to start working at the Mazankowski Alberta Heart Institute in Edmonton.

Christine Longridge, 50, has been charged with second-degree murder and possession of an offensive weapon.

The weapon was a knife, sources told CBC.

Police have identified the victim as 21-year-old Rachael Longridge. She just graduated from nursing school and was set to start a new job. (Facebook)

No history of violence

A police source said it is believed Christine Longridge was suffering from mental-health issues and that she had been "going downhill lately." But she had not been violent in the past "in any form."

Police have requested she undergo a psychiatric examination, but sources couldn't say if the exam is happening.

A vigil for Rachael Longridge will be held Wednesday at the Edmonton Clinic Health Academy, 11405 87th Ave., beginning at 6:30 p.m. An autopsy will be conducted Thursday.

A message on a GoFundMe page says it was set up to raise money for funeral costs and to help Michael Longridge get the support he needs "in this traumatic time." More than $29,000 has been raised.

Glen Dobranski, who wrote a story for the GoFundMe page on behalf of Rachael Longridge's first cousins, said Michael "stumbled upon the scene and now will have to bury his only sibling."

Rachael and Michael lived with their mother in the home near 122nd Ave. and 132nd St. Their father, Erin Longridge, died of cancer in December 2015.