Once in a blue moon something worthwhile gets posted on blue...
The difficulty with this observation is that the poster completely ignores the rest of the evidence. Sheila might very well have been struggling with mental illness and other issues in her life but such afflictions don't suddenly turn someone into a markswoman capable of wielding a rifle with supreme accuracy which hitherto they had never even handled. I'm sorry Lucy but in the real world these things just don't happen.
The observation reads rather like a novel. All those 'mishaps' certainly DID befall her, but not all at once. They may even have occurred over a period of 8 years. There also seems to be a penchant for saying how badly Sheila had been let down by her 'husband'. Colin WASN'T her husband. Hadn't been her husband for the best part of 6 years. If I can, for a moment, be brutally honest, it wouldn't surprise me it it was she, rather than the twins, who was "the millstone round his neck".................along with some residual guilt he may have carried about his treatment of her, naturally.