Dehydration is so common with captive iguanas that it should be listed as a common ig disease. All captive igs would benefit from being fed supplemental water. It would prevent kidney problems that so many of them have after they are about 8 y.o. Kidney disease starts out as sub-clinical kidney stress.
I agree with Rose. Plus, force feeding food is problematic. A non-eating ig has a reason for not eating. It could be environmentally stressed, have a bellyache, have an infection, have intestinal parasites, or be dehydrated. These things need to be treated medically, making force-feeding irrelevant and possibly harmful in most cases. But, in some cases, force feeding is the right thing to do, as when they stop eating for a prolonged time after surgery or injury.
Feeding 3 cc (3 ml) water twice/day for 30 days has a good chance to make her feel better, and can cause her appetite to return. Chances are high that she's dehydrated, since most igs are at least a bit dehydrated anyway. Feeding water isn't too stressful for her, and she will quickly catch on to what is going on, and hopefully start to cooperate. I've re-hydrated more than a few igs, without much fuss.
Put your thumb and forefinger on either side of her head, and use the popscicle stick method to open her mouth, then place the syringe tip at the back of her tongue, squeezing one ml of water at a time and then pause so she can swallow. She can hold her breath for a long time, and may hold un-swallowed water in her mouth for a while before she swallows.