No, no you can't accept that the only option is to fight. She's you! A dark, twisted version of you, but a version all the same. You have to believe that somewhere, deep down beneath the chemicals and anger, there's still some part of her that can relate to you. A part that remembers a time before whatever happened that made her like this.
You just have to reach it.
"You can't do this! It's evil!"
"Evil?" she shakes her head. "Evil is just a word. A word for a means that has yet to be justified by a worthy end. Stopping now? Letting my great work go unfinished? That would be evil. When I finally succeed at perfecting the process, it'll all have been worth it."
"But what about all the ponies you're hurting?" you plead. "What about them? Their dreams?"
"Eggs and omelets. Their sacrifice was for the greater good. Every failed experiment is a step closer to success."
It's not working. Your words just slide right off her. She truly doesn't care about the pain she's causing. It's... is this how ponies see you? The worst parts of you, at least? Magnified to an extreme where they eclipse the good. A single-minded drivenness with no regard for safety. An overbearing confidence that everything she does will work out; that failure isn't even a possibility. Loyalty to a cause, an idea, at the expense of everything else.
She doesn't just share your face, it goes deeper than that. She is you at your absolute worst. A mare condensed down to her most vicious and despicable traits. Pride. Callousness.
There is no reasoning with her. She's so stitched together by her own philosophy that if she were willing to pull the thread, everything that makes her up would collapse.
She has to be stopped. Not just for your own sake, but for all the other victims of her twisted experiments, past and future.
You set this thought in your mind as a focus as you concentrate on the fight ahead.