Last year, I notified my landlord that the tenants below me played their music too loud, and even though the frequency of occurrence has diminished, they still periodically play it so loudly that it comes through the floor. Also, one of the tenants had accused me of turning the hot water on and off, causing a fluctuation of temperature in her shower every time she uses it. She demanded I refrain from using all of my water outlets while she's in her shower. What's a person to do?
As unsatisfying as it felt in the past, your first line of defense is still your landlord. Have another chat. Restate the specifics of the music problem. And point out that you can hardly be expected to intuit when your neighbor is taking a shower.
If the landlord refuses to intervene, you have a couple of other possible courses of action.
You could threaten to move out. If you can convince a judge that the harassment from the neighbor constitutes an intolerable situation for you, you might be able to get out of your lease without being responsible for future rent. Of course, if you have a month-to-month rental agreement instead of a lease, you can leave by giving the proper amount of notice, which is 30 days in most states.
You could stay put. You might try to enlist the help of a third party to work out a resolution, such as a community mediator, if you can convince your neighbor to join you. The small claims court or your local district attorney in your county can refer you to neighborhood mediation services. Also see Nolo's Mediation Resource Center.