Is it ok to drive with two feet?

This has been a source of contention for my mother-in-law and me. She claims that since she learned to drive with a stick shift, she is used to driving with two feet. So in the absence of the clutch pedal, she uses her left foot on her brake. I told her that since I also learned to drive with a stick shift, I use my right foot for the gas and the brake, and my left for the clutch. So in the absence of the clutch pedal, my right foot still operates the gas and the brake, and my left foot stays idle.
My ex took my MIL?s side, and called me stupid. Any wonder the ex is the “ex”? Or that my daughter is too scared to ride in my ex-MIL’s car?