Problems with neighbor in a wheelchair?

My neighbor has a niece who is 40 years old and is mentally retarded and has cerebral palsy from birth. She was in some hospital, but about a month ago they brought her back. My neighbor put her niece on a small apartment between her house and mine (we share a wall) so she didn't have to hear her screaming all day, but now I have to hear her. I feel reall sorry for the woman, but she is screaming ALL DAY AND ALL NIGHT and the walls are really thin. Her screams are really disturbing, she sound like she's being skinned alive, and I can't sleep or do absolutely anything else because those sounds are just horrible. I know she must be in a lot of pain, but the screaming is constant and I really can't live like this, I'm having nightmares. I've asked people about this and they say I shouldn't say anything to her because I would be rude, her niece is sick and it's not like she's doing it on purpose, but I've been trying to get used to it and I can't. What can I do? I can't afford to move out.