1. The GCA is essentially the same idea as IQ.
2. Her Composite scores are all very good (except for "only" average on working memory), but also quite internally diverse. Most of them have about a standard deviation (or more) difference between the two subtests, which tends to make the interpretation of the Composite score a bit shakier.
a. Verbal: she did much better on verbal reasoning than on acquired verbal knowledge.
b. Nonverbal: she did much better on mathematical reasoning than on abstract-visual reasoning.
c. Spatial: she did much better on spatial reasoning than on design memory. (Notice that working memory was her weakest cluster overall, which suggests that it brought her spatial score down. See below on motor vs motor-free--that may also have affected this area.)
d. Processing Speed: she did much better on motor-free speed than on motor-involved speed.
So yes, this might be a low estimate of her ability, as she generally did better on the tasks with the greater reasoning demands (except for matrices), and may have had some scores lowered by relative weaknesses in working memory, and possibly fine-motor skills.
3. Processing Speed in this range is high even for a GT child. It means that tasks that require little complex thought can be completed very quickly by her. This, and Working Memory, are areas that are not as significant for overall intelligence, but certainly are useful for academic success. High PS often helps with calculations, extended writing, and managing heavy homework loads. These areas are also not computed into the GCA.
