My friends parents mistreat her! What should I do?

My friend always tells me how much her parents hate her, and how they mistreat her. I was over at her house not long ago, and I could see clearly that she was correct. Recently, her parents made her move out of her bedroom and into a teeny tiny spare bedroom (which they were using as an office) so they could use her bedroom as their new office. My friend also doesn't even have a real bed. She sleeps on an itty bitty air mattress that is uncomfortable, and has a hole in it because her parents refuse to buy her an actual bed. She's also not allowed to do nearly anything. :/ She can't listen to certain music (even artists like Taylor Swift are "banned"), she can't put up posters in her room, and she has to wear the same clothes every single day almost because her parents won't buy her new ones (yes, sometimes she will wear the exact same outfit every single day of the week). She also told me her parents call her fat, tell her she needs to lose weight, etc. She is definitely not poor, her parents just refuse to buy her anything and refuse to provide for her. I feel really sorry for her, and I want to do something about it. I told my mom all about it, and my mom wants my friend to stay with us for awhile, but she can't because she's allergic to cats and we have cats. D: What else could I do about this situation? Btw my friend is 15.