"I worked hard on her speech pattern, but not so much the accent because I didn't want it to be an imitation or a caricature," Melissa told ET.
The actress admitted that she teared up when we showed her a clip of her performance.
"I can't watch myself -- especially like that," Melissa said. "I think I was so focused on the details and trying to do a good job that it never hit me that I took this crazy emotional risk until I got home and went, 'What did I just do?'"
Joy tells the story of the Mangano family through four generations and details the rise of Joy Mangano (Jennifer Lawrence), who becomes founder and matriarch of a powerful family business dynasty.
"My agent received a phone call, saying, 'David O. Russell wants to meet Melissa,'" Melissa said of joining the movie. "It was all very hush hush and top secret, and I went, 'OK.' In our family when they offer a job, we always joke the answer is, 'Yes, how much?'"
Because this marked her first high-profile film role, Melissa understandably had butterflies as she undertook the task, but she found support in her castmates.