Welcome Martin, Charlie and Ziva. I agree with Julie about the mandatory photographs of the dogs. We can't get enough of them here
So far as the toilet training is concerned: I assume that you have had Ziva for about 3 weeks, i.e. since she was about 8 weeks old and ready to leave her mother and litter mates?
All pups vary in their learning curves and capacities to store their waste products and the frequency with which they need to evacuate them. Please forgive me for saying this, but I really think you are expecting a little too much from a tiny pup and that you should persevere with training without comparing Ziva's progress with Charlie's. Time, patience and praise are the requirements here.
Pups need to relieve themselves on waking, after food and before sleeping, so puppy needs to be taken out to do the necessary and lavishly praised when they have done what is required. I always gave them a little treat or biscuit after they had performed. It's good practice to give puppy a word to tell her what you want her to do. Anything will do that she is able to associate with what you want. My girl Holly P is almost 7 years old and a Pets As Therapy dog who visits hospitals and care homes. There is no way that I want to risk accident in either of the hospitals, so after giving her food and water I take her out to a patch of grass she is accustomed to using and give the command to 'wee please', which is obeyed in a matter of seconds, giving me the confidence of knowing no accidents will occur on the wards.
I also wonder whether Ziva is likely to learn from example from the older girl Charlie when she sees her toileting? As I said, time to learn, patience when she makes mistakes and praise when she gets it right should get through to puppy before too long.