A normal well-groomed woman, it's not like she can afford to fuck on the street for money and without a condom! Of course, I have fucked on the street, but of course with a condom. Even if you trust your partner, you're still getting laid on the street. I think in the cold and in the street it's not particularly pleasant!
Girls are girls, they like to be poked by dicks, and her brother's dick, even if it's her brother-in-law, is just a twig on which she can wiggle in a good way.