Trip to the vet ASAP. Call around for an exotics specialist or call your local exotic pet store and ask who they use. The gecko has all the signs of it, but it also sounds like it has been happening for a while (how long since s/he last ate properly?) Caught soon enough, there are people here who home treat with certain medications. I always suggest a trip to the vet because, especially if s/he has significant weight loss because it will take some support to get them back up and running again.
If you could have caught it before she lost a lot of tail fat, some vets will just do a fecal with a poo sample and it is much cheaper. I would strongly suggest a full vet trip in this case just to make sure it isn't multiple causes, like she has been stressed by the parasites and also then caught an infection.
I wish you the best of luck. We had our first little guy put to sleep due to parasites after a month of medicine and hand feeding a liquid diet when he just didn't bounce back (too young, bad pet store). There are lots of things that can be done, but sometimes all you have is hope and love. Good luck, I hope everything works out.
Oh, in the meantime you can get some vanilla (no other flavor, just vanilla) Ensure. It is a milk based canned drink for older people usually in the diet department. You can drop some on the geckos nose and get them to lick it off. It is high in calcium and protein, not to mention will help with dehydration. While in no way a cure, it will ease some suffering and offer some nutrition before the vet appointment.
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0.1 Albino Leo Gecko
0.1 Crested Gecko
1.0 Dear Boyfriend
Departed: Harvey and Spock