Dog mistreated and abused please help?

I placed an add on craigslist saying that my dad is looking for a puppy. and a woman calls and offers her 2 year old dachshund....saying that she is in a desperate situation and cannot have the dog anymore. at the time my dad wanted a jack russel puppy. so me feeling bad for the dog......went and took it home. i noticed that the dog looked like its leg had been broken and poorly healed. didnt think much of it at the time, bc at that time i thought she just had a bowed leg. well i kept the dog for a week. it became too much for me to have a dog here in my apartment.....so i called the lady and took her back. (stupid of me to do that) bc now that dog is in the pound and her add says "dog has been left in closet and fed only when owner wanted too" (i should have never gave her back to that lady, but i didnt know i thought her leg was just bowed, but now i suspect that she had broken it.......but idk) all i know is that i feel horrible for the dog....my heart wants to get her out before she is youthanized but i am in a pickle please help