The only reason she gets away with telling you what to do is cause you let her get away with it.
Be a man, man. Thank her for her opinion then just tell her you'll be doing it anyway. If she starts up with a fight or whatever, just walk away.
Meantime, save your money and have a "get the hell outa here" plan in motion.
Then if she ever actually follows through on her plan to kick you out, just leave.