This kind of revenge things actually happen quite often in real life as well, most of SA perpetrator don't get jail time, since most of the victim kind of forced to negotiate it instead of bringing it to court (and even in court sometime it ended with a "peaceful negotiation" instead of jail time). So after the SA perpetrator roam free, some of them seeks revenge toward their victim who report them, even more so if their career got destroyed and also mentally unstable like this woman for example.
And about the knife, that kind of knife are legal to have in Tokyo (but illegal to bring in public) and since it's small, I guess she hided the knife in her pocket before she uses it to harm Kaede (it looks like a foldable knife).
So in conclusion this chapter is as realistic as it can get with real life. The unrealistic bit part is the scene where Tsubasa jump in to save Kaede, it's unrealistic for someone non-profesional to react that fast in that situation but it's possible to happen.