Cheryl is 65 years old. She has been married to Jack for 40 years.

Jack belittles Cheryl in front of friends whilst drunk and says, "You know, I could get rid of you so easily. No one would ever know."

One day Cheryl comes home finds empty whiskey bottles and Jack asleep. She walks over to the bed, picks up a pillow and holds it over Jacks face, smothering him. Cheryl calls an ambulance soon after, and the recording of the phone call has her saying: "I just couldn't take it anymore. I knew that one day his threats would turn into action so I just put a stop to it."

Cheryl is charged with murder.

Discuss Cheryls liability for murder using the IRAC method.Refer to relevant legislation and case law.