You have to go back to square 1 I'm afraid, take her out in the garden for a wee & poo after every meal,drinking,waking up, and after playing, I find that using paper is very confusing for any puppy, it is actually telling them that it is ok to go to the toilet in the house! I train my dogs to 'perform' on command, I take them into the garden and say "be quick", when you first begin this wait until they are actually performing and say it in a calm friendly voice, believe me they soon get the hang of it! If you find a mess in the house, just calmly clear it up without saying anything to your dog then take her outside and stay with her until she has a wee or whatever, don't just leave her in the garden on her own. I hope that at this age you are not walking her too far as she is too young! at this age she should be going out on the lead for no more than 10 minutes at a time 2-3 times each day so a total of no more than 30 minutes and not all at once, their bones and tendons are very vulnerable at this age and she shouldn't be getting long walk until she is at least 12-15 months old, my GSD puppy is 10 months old and she gets around 45 minutes each day and she is still not allowed up and down stairs as they can cause themselves all kinds of damage!
I have kept GSD's for a very long time and have 3 at the moment, and a Border Collie.