First of all, I agree, with the onset of diarrhea a Vet visit is in order. She's not going to die from not eating for a few days, so don't get overly worried about that at this point. An adult Leo of a healthy weight can easily go a month without eating and not be in fear of immediate death. So, I'm not sure I'd try force feeding just yet as that can be pretty stressful to her. But you do need to figure out what's going on. It's great you are seeking help so quickly.
We could definately use some more information. How long have you had her? What substrate do you have her on? How do you measure the temps on the warmside of the enclosure? The temps on the warmside should be between 88-93 degrees measured on the top of the substrate. You say she's been have problems shedding, does she have a humid hide? Does she have unshed skin stuck to her anywhere? What do you feed her and about how much and how often? Is she housed with any other Leos? Answering these questions might give us some insight as to what may be going on. But please do get her to a Vet since diarrhea and laying in a water dish can be signs of parasites which can only be treated by a Vet.
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