Their arrangement is, in theory, completely consensual. Safewords, and limits, and all the usual stuff.
What she’s not telling him is that, the moment he orders her in for a punishment, all of that stuff disappears. The moment he tells her that she must be punished — no, even before that, the moment he gets the gleam in his eye that prophecies a punishment — her submission takes over her mind, and her safeword and limits and understanding that she has consented to this are obliterated. What she’s not telling him is that, for her, the game of sadistic master and frightened obedient slavegirl is real, and is becoming more real with each passing week.
In their arrangement, he always initiates the punishments, and she never refuses. It’s an arrangement she’d asked for, early on. It’s an arrangement he agreed to, with fascination and eagerness, but with more than a bit of trepidation. It’s an arrangement he thinks is a potential minefield. So he agreed to it only on condition that she absolutely promise to safeword if she needs to, that she promise to tell him immediately if he’s being too hard or too cruel.
For her, the moment her punishment begins, all of her ability to say “No” vanishes.
And that is exactly as she wants it.