Joni Mitchell performances are rare these days due to the legendary singer-songwriter’s health struggles in recent years, but she’s been making her way back into the public eye with a smattering of performances and the promise of a full proper set this summer. Wednesday night, Mitchell performed onstage once more at DAR Constitution Hall in Washington, DC as she was honored with the Library of Congress’ Gershwin Prize for Popular Song. Quite a few of her famous friends and admirers preceded her.