PLEASE CALL YOUR VET RIGHT AWAY!!!!!!
Both my 2008 foals had diarrhea and ended up in ICU.
My first foal, a very early premie had bright yellowy liquid squirty diarrhea, when it was cultured it was Clostridium Difficile. She needed IV fluids and three different antibiotics, Probiotics, biosponge, pepto, seramune, carafate. So did my second premie colt, but he wasn't as sick as Lucy was( she almost died)
You must be very aggressive with foals with bad diarrhea, they dehydrate quickly. Make sure she is nursing a lot too! PLEASE call your vet! I was lucky, they are both home now and doing well.
Robin