The 11-year-old plays the Twilight star's younger sister in the tear-jerker, and said their on-screen chemistry was just as real once the cameras were switched off.
"He's really fun and very funny, he was like a bigger brother except he wasn't mean - sometimes big brothers can be mean," she said. "He is very supportive and respectable, and easy to act with. I really admired his work from the beginning, and he was really nice to everybody."
The actress added: "It is extremely easy to bond with him. When we first met at the screen test, he suggested we should hang out a little and build chemistry but we never got to - it wasn't really necessary because we did a lot of waiting around on set, so we got to know each other then and goofed around."
Ruby - a Twilight fan - was amazed by the constant presence of fans and paparazzi around the Remember Me set in New York.
"It was crazy. From the time when we woke up, all these fans and paparazzi would already have surrounded the set. They were all over every scene. It was definitely a new experience for me," she recalled.