Are there normal round poops as well as the brown thick liquid?
As A&B says, true diarrhea is very serious in rabbits and often fatal. Rabbits can however have very loose stools without it being true diarrhea. You tell the two conditions apart by checking for normal poop as well as runny poop. If there is normal, round poops, it’s not true diarrhea. The cause is a less grave disturbance in the intestines, often in the gut microbiota. Because your girl’s puddle smells so strong, do you think it could be very liquidy cecals? Do you see any mucus or a gel like substance in the puddle?
Rabbit poop is rather complicated seeing that they produce two different kinds. Here is a good article by Dana Krempels a biologist who’s specialized in rabbits, it’s called the Mystery of Poop:
http://www.bio.miami.edu/hare/poop.html
A rabbit with true diarrhea tends to be very weak and wont eat or drink. The rabbit must be kept warm and rushed to a vet.