Jordin Sparks (left) and Whitney Houston, as Sparkle and Emma, in Sparkle
The moment she was told her idol Whitney Houston had died
, Jordin Sparks
broke down, locked herself in her hotel room and "cried non-stop," a source tells PEOPLE.
But the American Idol
winner, 22, kept her tears to a minimum on Thursday afternoon while paying tribute to the late singer at the Essence Black Women in Hollywood luncheon
at the Beverly Hills Hotel.
Speaking briefly about shooting the upcoming film Sparkle
with Houston, Sparks grinned and told the room, which was packed with Oscar contenders and others who included Viola Davis, Octavia Spencer, Emma Stone
, Paula Patton, Pam Grier and Kerry Washington: "The first day she got [to the set] she's scolding me, and I'm thinking this is the best day ever. She went from being this unreachable supernova pop star to my costar, friend and someone who was like a mentor to me. It was a gift and an honor to play opposite Whitney Houston in the film."
Besides her brief speech, Sparks also performed "Look into Your Heart," a song from Sparkle
"When you see Sparkle
, you will be so happy to see the joy that is on her face," Sparks said about Houston. "Everyday started with Whitney saying, 'How are my babies doing? Are you guys good? God is good.' It translates on the screen."