Hi Patti,me too.Right-handed but hold cig with left hand. Only the slightest tinge of nicotine is visible to see the difference in my right and left forefinger.
Sheila smoked thick cigars as well as her cannabis,so markings would have been more pronounced I would imagine. She must have smoked both to " the bitter end " in order to have had staining of her finger/s.
I've often wondered if there'd have been a strong smell of cigar smoke when the police entered the farmhouse.It's never been mentioned,unfortunately,as it would have been another indication that Sheila was " up and about ". Though,saying that,the police would have related a cigar smell to a male and not necessarily a female.