Her name is Lydia Callas (or Lydia Callis).
when watching this, i wondered if she's gonna lost her job, because she certainly stole the show. People are watching her and her expression instead, and the actual message content is lost. So, this lead me to think that perhaps it's common that sign language interpreters are supposed to be completely expressionless by the profession's etiquette, and whether it's common knowledge or joke in the community that attractive girls can't have sign lang interpreter job.
The language she's using is ASL.
American Sign Language (ASL) is a sign language, a language in which the hands, arms, head, facial expression and body language are used to speak without sound. Like other sign languages, its grammar and syntax are distinct from any oral language, including English.
Note that, there are quite a few sign languages, and they are mutually unintelligible. Just like normal language, they may have different grammar structure, vocabulary, etc. Quote from Sign language:
Wherever communities of deaf people exist, sign languages develop. Signing is also done by persons who can hear, but cannot physically speak. While they utilize space for grammar in a way that spoken languages do not, sign languages exhibit the same linguistic properties and use the same language faculty as do spoken languages. Hundreds of sign languages are in use around the world and are at the cores of local deaf cultures. Some sign languages have obtained some form of legal recognition, while others have no status at all.
Update. Apparently she became a instant net celebrity. Twitter is flying with “#SignLanguageLady” tag. However, she isn't present in later press conference. What's disturbing is that, according to some online blog, her tweeter account disappeared after the incident. What happened to her?
thanks to F Lengyel.