Perhaps being at the farm (where she was less happy) and around her mam (with her religiosity etc); and the rejection by Colin; and the recent contact with her birth mother; and the reduction in her anti-psychotic; and fact there were farm weapons - became a lethal combination regarding her mental health. Factor in an added conversation about extra assistance for the twins etc (which took place at the farm - not in London).
I must say when I found my birth mother, granted she didn't want to know me it was one of the most upsetting times in my life and I had a lot of conflicting emotions, and was very up and down, don't forget Sheila had also had a miscarriage and blamed herself, another trying time for a woman, she may of felt her remaining children she was going to lose, her parents didn't understand her and the rejection from Colin after the rejection at birth would of severely impacted her self worth, couple this with a severe mental problem and mind altering drugs, it's a recipe for disaster. The most sane of minds would probably of found this difficult to deal with let alone a paranoid schizophrenic.
