We're working our way through a similar situation with our dd10. Our oldest (12), too is HG and very academic. Our little one doesn't appear as obviously gifted.
In our dd's instance, she has been tested twice on the WISC. Once the VCI and PRI were very high 99th+ and once the VCI was very high 99th and the PRI was in the 75th. Both times, WMI and PSI were avg.
The first test administered on the WISC is the block design, which is timed and is part of the PRI index. That would lead away from depressed scores due to having not yet warmed up to the tester in your dd's instance b/c she did very, very well on PRI (unless, of course, block design was lower by a lot than the other two pieces of that subtest). If block design was a lot lower, that would add to the insight that processing speed is an issue for her.
Your description of your dd sounds a lot like my dd10 as well -- very verbal, always "on."
Beyond that, I'm not a lot of help! We are looking at anxiety, divergent thinking, and possibly ADD with my dd.