Suggest Treatment For Excessive Loose Motions In A 2 Year Old

My two year old had has horrid, foul smelling watery poop dor 4 days now. We ve tried the BRAT diet, she had had plenty of bananas but nothing is clotting up her poop in the least. Her appetite has been I ll. She has had some solid food but her poop still remains like water. And clay like? A mix of both. It is a light light tan or gray ish color. Her dr had me get a probiotic but it has not helped either. I am taking her in tomorrow to get thr specimen cup for them to sample. However I am getting a tad more worried the more this goes on and I m reaching out for some input if at all possible.