Yes, please take her to the vet, from the first time I saw her tail something didn´t look right, that´s why I asked if she was eating fine, there could be many many causes, from parasites, bacteria, cryptosporidiasis to gastroenteritis and so on, it is virtually impossible to diagnose without a veterinary check, you have to do a fecal test and have her checked by a reptile specialized veterinarian asap, she is sick, that´s for sure and she simply won´t live long without specialized care .... it is sad, where did you get her from? What heat ource do you provide for her?? Because if we start from the basics, a gecko that doesn´t have the right temperatures can´t properly digest ..... I am asuming she is sick because of the thinness of her tail