Do you know what her background is? If she was kept in a cage all her life, she got used to eliminating there and her instinct to keep her "den" clean is gone. Crate training usually doesn't work with these dogs.
How long are you gone? I think it's unreasonable to expect a dog to stay locked up in a crate with no room to move around if it is for the whole workday. An exercise pen with a enough room for a bed and pee pads is a much kinder solution.
I always recommend the book Secondhand Dog to anyone who adopts a rescue:
Amazon.com: Second-Hand Dog: How to Turn Yours...