Is it possible to agree on feasible expectations with my supervisor or should I surrender to her demands?
She has the right to make a numerical suggestion, since the guideline does not specify any number. The first thing is to determine if this is feasible. Check the thesis and publications of other PhDs coming out from her lab and if this has been the norm, then at least you know that i) it's been done (whether you can or not is another matter) and ii) she is not making an unreasonable request.

The second thing is to determine if you have the drive, time, energy, and determination to churn out five papers with publishable quality in three years in your field. And thus far is it likely to happen if you're 4 months in and she has only been treating you as a RA.

The third is to check if you really like to do this PhD with her. Your questions have a lot of resentments and mistrusts, on top of negative wordings such as "surrender," "fight the battle," etc. Do you really want to work with her? Or are you victimizing yourself a bit too fast too furiously? You'll need to ask yourself that. If you're only 4 months in and already hating her at this extend, I'd frankly suggest think, hard, if you want to stay.

Lastly, whatever the agreement will be, have it clearly stated in writing: How many, in what time duration. And what is considered "a paper." Don't guess her meaning by saying "preferably published". Define the meaning: is it a chapter with publishable quality? Is it a real submission with at least one round of review? Or is it actually published?. Notice that if your work does not pan out and you never have the papers put together you may just end up miserable and PhD-less. Use that as the benchmark and negotiate (not fight a battle.)