I live with my mom-in-law. She said that she will come into our "area" whenever she wants, what do I do? do?

you say she is a stubborn as a mule, i suspect you are just as stubborn as a mule; hence lack of compromise on both sides. seems to me that she has every right to lay down rules, its her house. if you don't like it then move out. suck up or ship out. you are not paying her anything, think yourself lucky that she lets you live there sponging off her.