Well, some grow super slow and don't eat a lot but the gecko shouldn't be skinny. At lower temps they eat less (but again shouldn't be skinny).
If it is parasites I'd be expecting weight loss and lethargy as well as odd/runny stool. However, it wouldn't hurt to get a fecal done.
Is this gecko housed alone? If not it may be being bullied.
You can try hand feeding... but it sounds like she is a pain to handle and it is stressful. You can offer crickets to see if you can boost weight. Try the flavored diets maybe. If you absolutely have to, add a bit of baby food (peach works good) to flavor her diet to see if it gets her attention and once she is eating it wean it out- that's how I eventually got my male to switch to pure CGD and eat normally.