If I say yes, what will you do when she moves your furniture and puts hers back? This is a foolish argument with no winners.I am really just asking whether I can move her things if she will not
You can both put the other's furniture in the basement and put yours in the main living space. Then they other can do the same thing. Every day until somebody moves out, you can move furniture up and down the stair until somebody just gets too tired to keep up the foolishness.
Each of you would be liable for any damage you caused to the other's furniture.
Unless you have some sort of agreement between the co-tenant, you have a problem without a solution.

