That kitten needs a vet now - she is going to get dehydrated. Stop mixing water with dry food - it's sprayed with fats to make it more appealing, and quickly becomes a 'bacterial soup' when water hits it. You may be making the problem worse, Avoid foods that contain corn, as corn is not well digested by cats and that can contribute to very loose stool. The dry you chose is sadly full of corn. Yes, she has technically been weaned to early as it's during this period of 8-12 weeks where they learn important things like playing with claws in, not to bite, and mastering litter box skills. Feed her a quality canned kitten food that has a real meat (not by products) as the first ingredient, and ideally what she had been fed prior to getting her. It can be anything - worms, coccidia, giardia most likely. Get her seen TODAY not next week as you may have a very dehydrated and ill kitten by then. Be certain to take a nice fresh stool sample with you and ask specifically that it be tested for coccidia and giardia - those require a microscope slide, and are often not tested for as they are not part of the normal search for worms or worm eggs.