Can someone help me with my Bunny?

Okay, so I feed her regular bunny food (you know, the pellets), Oxbow Timothy hay, and tap water. Her poop is a little runny and squishy, and she keeps stepping in it. She's acting totally normal, but I'm a little worried because another rabbit I had named Ollie had died of a disease after the one day when he had diarrhea. Is it true that I should stop feeding her pellets if her poop is a little runny, but she's still acting normal?