Please help!

So long story short my almost 4 year old eats a bunch of shit she shouldn't it started with dirt/rocks/sand anything she could pick up. Normal toddler experiences but then she started eating shoes paper crayons large amounts or dirt, even slate once. But today about tipped me over the edge. She is fully potty trained can wipe and wash her hands alone no problem so tonight before bed I say go brush your teeth and pee mommy will go put your heat on and whatnot but she doesn't come out so I go into her play room she is hiding behind her recliner when I look over the chair she has a cup with toilet water (I'm hoping just water) and toilet paper. Well I'm not proud of it but I'm like wtf? So I grab the cup and start crying (I'm pregnant so my emotions are crazy) about how it's yacky and there's germs and that she poops in the toilet and her response to all of this is "but why" repeatedly. I have tried everything we got rid of plants try to keep shoes out of her reach. Only colors with us there. I've taken her to a dr who ran labs and said she doesn't have any deficiencies and she may have an eating disorder called pica but that's not very helpful when my kid is going to get sick from the shit she puts in her mouth. I'm so heart broken and I feel like I'm failing as a mother. I want her to be healthy and happy but I don't know how to help her. Please anyone that has been through similar things any advice would be appreciated via /r/Parenting http://ift.tt/2DAmhBj