The lady with the guitar is Ashleigh Ball:
She’s out front of the Vancouver-based indie band Hey Ocean!, seen here in a stripped-down version of “The Beatboxer Who Broke My Heart”:
This is not the version which appeared on their 2008 album Stop Looking Like Music. Then again, the last time I heard her voice, I was looking at something like this:
Either one of them: in the current series, she voices both Rainbow Dash and Applejack. And, lest she become overrun with free time, she’s also the voice of Allura in the current Voltron Force.