One: Your gecko has become impacted and will not eat because it is full of sand, bed o beast, spagnum moss, or woodchips, or calcium carbonate or whatever loose substrate you might use.
Two: you are smart and have your geck on a safe substrate, and she has just gotten sick. If this is the case you have a huge chance of getting her better. She needs to go to the vet. In fact I would say the pressence of diarhea would indicate that she is sick. Probably bacteria, or worms of some kind. GO TO A VET!!!, they could do a very simple procedure to see if she is infected with parasites. Please let us know what the vet says, if your not going to take her to the vet your not being a very good person. She has been with you for six years I think all that joy that she has given you would be worth the sixty to 100 dollar vet exam fee.
PS not meaning to sound harsh, but please take advice
