Sometimes my downstairs neighbor's stereo is audible in my bedroom at night when I'm going to sleep. I just turn on a window fan -- in cold weather, one sitting on the floor rather than in the window! -- and that whoosh nicely masks the unwanted music.

But as for the trains, I agree with JohnInKansas that after a while your sister probably won't notice them. I've lived for twenty years now about a hundred feet from an active commuter train line and the only time I notice the trains is if one happens to be going by when I'm out in the parking lot. Otherwise my brain just tunes it out.