OP isn't very old either; 25 by what I think I read. What if something happens to her? As I said before; I didn't say to actually have the guy stay there - I said to point it out to her that he can stay with her. If she felt uncomfortable about the guy (which sounds apt); sending him to her sister? Shit move. It's just putting her in danger. And she didn't tell the sister until he is halfway there; shit move again. It's forcing the sisters hand so she can't say no.
And for the record - what you are saying is one women who isn't much older should potentially put herself in harm's way because the younger sister sent a nearly 40 year old guy over to her house. As OP said - her husband is out of the house at 7am... When she is then stuck alone with him. You think being five years older is going to protect her somehow?
And you want to know one reason why women get assaulted? Because we are told to 'be nice' and crap like you are saying. OP is also a young women - why the fuck should she put herself in danger because her younger sister was an idiot and sent some strange guy to her house - and then couldn't be bothered to tell her for an hour?