Say what you like but NOBODY saw this coming. Sheila had part of her medication intramuscularly simply because she couldn't be trusted to take it orally ( what does that tell you ?),and as it was,what bit of Haldol she had left in her system was as good as useless when she was smoking heavily on cannabis ( hence her nicotine-stained fingers ) which would have counteracted any anti-psychotic medication.
Jeremy only found out about the extent of her illness by reading up about it in prison,and the police wouldn't have known,they're only just learning about mental illness now 30 years on !!