But she doesn't want to harm him, just help him as long as she thinks he isn't trying to kill himself. Plus the first time she almost killed him she didn't have much reason to do so, since he was about to hang himself. After that she "realized" that he only wants to make himself taller, so she doesn't object when he tries to hang himself.
Actually, that doesn't make sense with any other explanation. Why would she try to pull him down the first time yet help him later if it wasn't because she convinced herself that he's trying to make himself taller?