I had a terrier do the same thing....just stop eating suddenly. Had to take him to the vet and it was the pacreatitis that the vet mentioned, plus an infection of the spinal cord. I would agree that the vet can help find out what is going on with your pet whether it be a blockage, pancreatitis, or any other symptoms. Especially since she is usually happy to eat and not eating well is a change for her. I know for my dog, that is the best clue that he is sick...since he can't talk to tell me that he's not feeling well. Best wishes for you and your dog!
It may be important to take her to the vet just because this behavior is so unusual for her. She may finally have eaten something that will not pass through her digestive system, or is causing an obstruction, or may be causing pancreatitis, or it could be something unrelated, such as impacted anal glands. Pancreatitis is a severe, debilitating disease and requires in-hospital care, whereas anal gland impaction can be relieved by an anal gland expression.
Please take her to the vet just in case.
oh and dont give her any laxitives or anything, because that could possibly make the "blockage" tear the intestinal wall, if it is a blockage
she could possibly have a blockage in her intestines, my pug rockstar loves to chew on everything, including my furniture, and i just recently had to take him to the vet, he had the same symptoms, and the vet found couch cushion blockin his intestines. They gave him IVs all day every day for about a weeks, and it passed. But it all depends on whats blocking them. Take her to the vet asap