I found the book mentioned above really helpful, also "disorganized children":

http://www.amazon.co.uk/gp/aw/d/1843101483

This one is not aimed at giftedness but at multiple disorders and how they present - including discussing that a child who's borderline for multiple issues can be impossible to diagnose while also being as impaired as a hold who has a classic presentation of a single condition. My DD is barely diagnosable for CAPD, dyslexia, SPD, ADD, receptive language delay, developmental coordination disorder (she doesn't quite meet diagnostic criteria for the last two, but she's close)... None are severe on their own, together she has a LOT of challenges, which I am no suggesting is the case for your DD, just that the single chapter per condition is handy for thinking "Nope, nope, maybe, yes, nope...." For us the pattern that emerges is that all her yes/maybe issues are related to/symptoms of or comminly comorbid with Aspergers.

From what you've said here selective mutism, social anxiety and CAPD are the things I would be reading up on.

We had our second DD assessed for selective mutism a few years ago, the conclusion was shy, but not unable to talk so much as unwilling to talk. The psychologist we saw was spot on with all the other traits she observed/extracted from DD in their time together so we went with that. Time has shown the "rude not anxious" assessment to be correct for our DD, but certainly selective mutism is a very real problem for those that have it.