If that isn't an appropriate thing to measure, what is?

The mass of each pill of SSRI as you steadily taper off your dose. ;)

You start the process only after you have successfully convinced your oppressor that you have submitted to their will. You then take whatever measures necessary to convince them that you are going along with their plan and do whatever you can to thwart it, within the limits of what you think you can get away with. In this case it is fairly difficult to ensure that a victim has swallowed a tablet without intrusive physical intervention.

Disagreement, argument, defiance and even 'oppositional' behaviours, undesirable as they seem at first glance, are actually a something of a privilege that you are granting. In the absence of bystanders whose allegiance could be manipulated these all imply that you trust them enough for honest engagement to be in your interests. You (you being a general hypothetical entity in related circumstances) don't owe this kind of intimacy to anyone, particularly if you suspect their response will be to have you forcibly sedated!

There is a time and place for honest assertiveness. That time and place can be loosely described as 'when it works' (with a whole bucket load of caveat). In all other situations lie through your teeth, hide the pills near your cheek and spit the unsavoury incident and unwanted pill out of sight and mind at the earliest possible opportunity. Better yet, use the Prozac to spike her coffee. That'd almost certainly do more to enhance your personal wellbeing than taking it yourself.