for me, it wasn't so much a gender issue or a strength issue but a vulnerability issue or the appearance of vulnerability. where i was, at the end of a dark road (literally) it could easily be that someone found himself/herself/themselves at the end of the road and not wanting to treck back, looked for a place to stay. totally understandable.
if there were guests in the library and/or on the porch, and someone arrived, i was likely to accommodate them. but if the place was quiet, the guests up in their rooms, no one in the common areas, probably i'd just lock up and not be answering the door.
there was another thread about security a while back ... not sure what the title was ... and i mentioned that i did have a tiny pepper spray and also a baseball bat ready to hand. not sure these items would be helpful but i like to think so.
years back, i was working someplace else (not a b&b, but a clothing store) and we were robbed by someone who was very agitated. he became angry that there wasn't much cash to be taken. smashed a few things, but not me, thank goodness. that is the type of scenario i was concerned about when running the inn alone. not much cash around but possibly someone would THINK there was.
all innkeepers, regardless of their gender or whether or not they work alone, should take a moment to evaluate their own security and that of their guests. we each have to do what is comfortable for us. but i wouldn't recommend that anyone open their door at all hours of the night for unexpected guests..