It is not clear from your question what steps you take when there is a problem and that certainly plays a part in your chance for success. The description you give can only send one message, she does not feel that there is any reason not to poop or pee outside the cage. Just as there must be positive reinforcement when she does the right thing there has to be a rememberable correction deterent when she does not. Please let me know what steps you take when she gets it and what steps you take when she doesn't and I will try to help.
The use of "bitter sprays" on the pad or in her cage will often backfire since they can signal "stay away" from the very area you want her to use.
Please let me know how old she is and the steps you take.