8 year old puppy mill female not house trained any suggestions

We adopted an 8 year old female schnauzer 10 days ago and she isn't house trained. I take her outside every two hours are so and although she will urinate and sometimes have a BM she would just as soon do this inside. She has lived in a cage her entire life. I am being patient but do you have any suggestions? We have a poodle and another mini that she can learn from as well.

NOTE FROM LINDA AND MAX:
Hi there, good for you, taking in this poor girl.
It sounds like you are doing all the right things - taking her out regularly, especially if she goes out with your other two and can follow their example.
The key is patience, she is middle aged and will not unlearn her previous habits quickly, but with your patience and the example of your other dogs, she should become fully house trained.
Make sure she goes out after meals and drinks and try having a word which she wil learn to associate with urinating.
Speak in encouraging tones and reward her immediately with a treat whwn she goes. Reward-based training will be the quickest method.
Hope this helps and good luck.