If the waste is whitish and mostly liquid, most likely it is just the gecko's urates, a form of urine that reptiles pass and it's normal.
Have you been weighing her to monitor her weight? If not you may want to try purchasing a gram scale to keep an eye on her from week to week to ensure that she isn't rapidly loosing weight. If this is the case you may want to take her to a local vet who is familiar with exotics to have a fecal float test done to rule out any possible parasites that could be causing her to loose weight and her appetite.
Is this a young gecko? If so she may be eating small amounts of food when you aren't looking and it may not seem like she is eating much. How much food do you normally offer her when you aren't hand-feeding her and how is her enclosure currently setup? If you aren't seeing normal droppings you can try moving her to a more sterile environment with paper towels as a substrate liner and minor decorations to make it easy for you to view them.
It's also worth mentioning that if your house is relatively cooler this time of the year then it may just be slowing down her metabolism, which would cause her to eat and poop less often. This time of the year I allow the room that all my geckos are kept in to drop considerably and they noticeably eat and pass waste less than they normally would in warmer temperatures.