I just came across this thread. I hope the OP's sister is doing better. I lived in rentals so could not engage in major structural renovations. I found relief running a fan on my bedside table right next to my head. It not only helped to mask noise, even sharp noises, but subconsciously focussed my mind on the sound of the fan. Sort of like hypnotism or response training. The relief from running a fan is so palpable it noticeably calms me down. Unfortunately I can't sleep without it tho, even in winter. I now use a good ceiling fan which can run in reverse in winter.