Disclaimer: my biases where I probably assume people are like me more than it's true
> But then there's also this thing about being explicit - if I don't say, "HEY, you are hurting me!", she doesn't know.
There's an additional benefit to being explicit: it doesn't only cause both parties to know $foo, but also to know that they both know $foo and all higher iterations. Being in a state where you both know $foo, but don't know that the other knows $foo or sth like that becomes weirdly complicated socially (someone once gave me a very intuitively obvious example that illustrates that, but I sadly can't reproduce it).
(My bias is probably in the extent to which that kind of complicated weird miasmatic situation is undesired.)
Also, I find it funny that people often think of the ability to tell that what you're doing is hurting someone else as a universal ability that you can just have more or less of. I think there's a very strong component dependent on the target person here, and some part of what people think of as this universal ability is explained away by similarity to the target person.