There are a few things that can cause growth stunting.. eventually if it is not eating proper it can lead to other issues. Parasites are common in farm raised iguanas. These will leach nutrients from the food, also affects their diet. I would have a fecal check done. It is the same tests vets give to any other animal... even people. The vet will need a fresh sample.
Proper temps and lighting is important too. Temps should be mid 90s at basking zone, cool end low to mid 80s... tanks are horrible at maintaining temps. You should have a uvb bulb and set at proper distance.. unshielded by any covers or fine wire mesh. Mercury uvb bulbs have a much better uvb output than tubes.. but if you buy a screw in type coil uvb bulb... they are absolute shit.
And then there is stress.. how is the cage setup? Is the iguana near an area that has a lot of people traffic or other pets? If so you might want to move it. Also glass tanks are very well known to reflect the iguanas image to its self making it think there is another iguana there... they are solitary creatures and freak out easily. You might want to place cardboard around the glass. Until it eats properly you might want to reduce the human factor and limit your interactions. From your description on its current interactions that is a defensive/scared shitless iguana so when its eating properly start grabbing her as quickly as possible... dont let the whipping back you off or it will learn to do that. Simply hold her until it is breathing normally and try some fruit snacks by hand. Just remember time and patience. If you have a smaller room like a bathroom that is escape proof try sitting down and let the ig wonder around.. eventually it will realize you mean it no harm.. presently you are a predator in its eyes.
As far as foods you feed now.. stick to greens and veggies. They can be picky on how large the food is cut up.. so try different sized peices.. it might help to separate the food a bit to see its likes and dislikes.. you can worry about feeding needed disliked foods when its nice and fat. Food color is a factor too.. my uromastyx where not so crazy of typical orange carrots but when I started feeding multi colored carrots they dove right in. I tend to use a food grater when I prep food. Works great for squashes too which igs love..