Selfish people

Lately, I have a new neighbour who has been adding unnecessary anger and stress to my daily life in apartment. She has this habit of locking my side of the bathroom door, hence restricting my access to the bathroom. And she does it even though she is not using it, and she can leave it locked until I could bear it no longer, and have to either unlock it myself or knock loudly for her to know that I need to use it. I don't understand why someone can be so self-centered? This is a common bathroom, and it should be shared between both residents. While I always make an effort to restrict my use to 15 min per time, I don't understand why she can use it for up to 30min during the morning hours. Ever since she moves in, I have to wake up early and make sure I use it before she uses it. Otherwise I will be late for work. I'm not happy here.