Amazing
As a serious devotee to Bluegrass and traditional folk music, I can say she has easily one of the purest sounds I have heard. Haunting.
If the acting gig doesn't work out, she has a future as a singer
Well she does have a career as a singer.
She got the job in Songcatcher because she had been a member of the Children's Chorus at the Metropolitan Opera in NYC. She'd left shortly before because a growth spurt when she was about 12 meant she outgrew the children's costumes. Because she'd loved performing she was taking acting classes and going on auditions. So when the filmmaker contacted the Children's Chorus to find out if they had kids who could sing and act, they suggested her.
She's done some singing in two other films. One is an odd indie made a few years after Songcatcher called Nola. Her songs in that one are more pop ballads. She also played the lead role of Christine in the 2004 film version of The Phantom of the Opera which is more of a musical theatre/popera style of singing.
She's also released some solo music. Her first album "Inside Out" came out in 2007. It was songs that she'd written herself and was sort of ambient, vocal, pop. A lot of people thought it had too much synth but actually she recorded each vocal track individually and layered them so that it filled the track and even stood in for instruments at times. The first track on the album "Slow Me Down" is actually totally a capella. Emmy's voice replicates all the instruments. One song, "The Great Divide" she claimed was very influenced by her experience with folk/bluegrass music on Songcatcher in term of the plaintive tone and vocal flips.
http://www.youtube.com/watch?v=miBvlfArLpo
Later that year she released a EP with several holiday songs called "Carol of the Bells".
Last year (2013) she released her second album "Sentimental Journey" which features American standards from the 20's through the 60's. It's a more traditional album than her first, but it's the music that her mother played around the house when she was a kid- including some that her mother sang to her as lullabies. It features songs a couple of songs with roots/bluegrass influences though the overall tone is more jazzy.
http://www.youtube.com/watch?v=5VPdlAIr24M (interestingly she sort of de-countrfies- is that a word!?- Willie Nelson's Pretty Paper)
http://www.youtube.com/watch?v=QDwRgnQlxHw (this Connie Francis song seems to retain the country influence)