WARNING! Very long answer.
As I have said, I have no deeper information on the inner workings of the game. Just rough understanding from hours spent playing it with different origin stories.
That said, from what I experienced, there is some stuff your sister warns you about that is really true. And not only on the bus.
It is just strongly dependent above all on two of your character's attributes: Desire and Allure. Allure regulates how eager the men around you are willing to mingle with you. Desire regulates how much you are willing (or unwilling) to reject their approaches. The other attributes, Confidence, Fitness, etc. and alcohol also play a role but they aren't as obvious.
Take for example the school bullies. They will harass you as long as your confidence is very low. I don't think they will rape you since I've never seen it happen, but I'm not sure because one of my priorities is always to increase confidence as fast as possible. Perhaps I will try the Bambi setting next to test what happens.
But yes, there are situations where you will be raped on the bus or in the park to name just two of the more probable locations without the possibility to offer resistance. Just be really alluring (400++) and have your desire on overdrive (300++ or better more. I think my "best" value was way higher. Don't remember exactly, but perhaps higher than 1000.) Being drunk and on the move on weekends after midnight helps a lot.
Try to serve in the pub on Saturday until it closes around 3 AM on Sunday. Prepare a really revealing outfit to switch (or be switched) to. If some of the customers invited you to drink with them and spiced your drink with a LEBO, the probability for you to be attacked and unable to reject the advances is very high. You can also increase your Desire to your max pretty easily by wearing an anal plug. This can be sometimes found or bought.
The probability to be forced to have sex is also very high during the Haven mission. But here, again, I managed to escape this fate even when plying with a Bimbo origin. Just had to reload once or twice.
I am an old school role player and thus try to immerse myself very deeply in the role of the character. Therefore I always try to avoid unwanted sex in this game. Partly because of the game's setting being as it is a caricature of a misogynistic world. So perhaps my view is somewhat distorted.
But I think it's true that the world of "The Fixer" is not as brutal as it is communicated. A lot of really negative encounters can be avoided if you are not front-up reckless. Possibly Sam_Tail has either defused the game since the initial release, where the sister was conceived, or simply didn't find the time to implement the more brutal aspects yet.