Kelli O'Hara and Ken Watanabe will star in the Rodgers and Hammerstein classic.
Check out photos from the celebration at The Public's Delacorte Theater.
An onslaught of Broadway's best have joined the social media campaign to lend their well wishes as the young girl undergoes brain surgery.
The Cabaret director was honored at the Hammerstein Ballroom with the Jason Robards Award for Excellence in Theatre.
Donna Murphy, Kal Penn, Tim Gunn, and more will take part in the event.
Other performances will feature Michael Mayer, John Patrick Shanley, and Jonathan Groff.
Manhattan Theatre Club and MCC Theater's coproduction also stars Danny Burstein and Victoria Clark.
The new musical is written by Lisa Kron and Jeanine Tesori.
Other notable guests included Into the Woods costar Chip Zien and Gleason's husband, Chris Sarandon.