12. Sheila then washes or cleans herself, and wipes the rifle action, then deliberately shoots herself. She has a flash of clarity, and is ashamed of what she has done, therefore she doesn't commit this act in the twins' room but assumes she faces a long prison sentence and public opprobrium, etc., and thinks suicide is now her only way out. She cries. She knows her body will be found - obviously - and looking clean is important to her.
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You believe she washed herself afterwards. Lucky she had time prior to the police arriving.
Her nightdress was not damaged. So only correct she was also clean.