To add to what others have said...
How often are you taking her outside?
Take her out every 30 min on the nose... do this for days. Its a pain in the butt, but it works. Then, to be blunt... praise the living hell out of her EVERY time she goes outside. BIG TIME praise. Dogs thrive on praise. They live to please the alpha of the house. Your neighbors may think you are nuts... but it works. Take treats with you also, but only small pieces (or even cut up chicken). Dont want a fat dog.
That being said.. you MUST become the alpha of the house. This is done by respect NOT fear. Do not beat or scream at her if she messes in the house. Try your best to catch her in action and immediately get her outside.
DO NOT rub her nose in it, etc.
There is a HUGE difference in a dog that respects its owner and one that fears its owner. You want that respect.
Also, use the same door every time to go outside. Make it a routine.