Rita Ainsworth (リタ エインワーズ Rita Ainsworth) was Mashiro Shiina's roommate and handler when Mashiro was in England. She was jealous of Mashiro's art talent, and so advised Mashiro to draw manga, but she later regrets this after finding that Mashiro made a big hit on her manga, and comes to Japan to bring Mashiro back to England. After realizing Mashiro's determination, she gives up and returns to England with Mashiro's father and resumes to study art. She usually argues with Ryuunosuke Akasaka.
She falls in love with Ryuunosuke and kisses him near the lips when leaving Japan, which makes him pass out. The second time Rita kissed Ryuunosuke was in Episode 24, though Ryuunosuke was more cautious. While Ryuunosuke is cold to her and keeps letting Maid handle her email, this only increases her determination and makes her constantly argue with Maid over the Internet. In the fifth novel, she visits Japan again to give Ryuunosuke Valentine's Day chocolate, and catches a chance to kiss him on the lips this time, which makes him pass out again.
Rita believes in chivalry, given her English heritage, and at times, implicity imposes it at the male residents of Sakurasou. She is a persistent person, as shown by her determination to bring back Mashiro Shiina to England, falling for Ryuunosuke Akasaka, despite failing somewhat. She, however, makes this work with her successes and talents, being determined enough to continue painting, after realizing what she really wanted.
Rita cares deeply for Ryuunosuke and the Sakurasou residents, despite not being a resident herself. She may be considered "Sakurasou's eighth resident", as she was involved in certain historical events that transpired at the dormitory.
Rita is also a great painter, perhaps only falling second to Mashiro. In the anime, the painting that Mashiro was looking at, was Rita's own painting.
Originally, Rita hated Ryuunosuke for being too harsh to her when it came to details regarding her wants and expectations. However, she ended up admiring him, as she loved the wisdom that he spewed (and the fact that he was also the one who made her realize what she really wanted). Soon, Rita becomes interested in him and falls for him, despite Ryuunosuke's gynophobia and Maid-chan's resistance. Despite their relationship seeming one-sided, this pushes her determination to win his heart someday. Of all the residents at the dorm, she cares for him the most.
Bluntly speaking, Maid-chan hates Rita, because she's jealous with Rita's advances with Ryuunosuke. This hatred comes to a point wherein she intercepts Rita's emails and calls, and refuses to patch Rita to Ryuunosuke when she calls him. To make matters worse, Maid-chan even asked Sorata to go to England and kill Rita as a sign of his gratitude (after Sorata thanked her.)
However, Maid-chan is not that selfish with her. At one point, Maid-chan revealed Ryuunosuke's past, even if she knew herself that this was against her own code.
Rita holds a special relationship with Mashiro, since they were both cousins back in England and that Rita was Mashiro's handler. Despite this fact, Rita resented Mashiro, as it appeared to her that Mashiro only cared about herself and not about the confidences of other art students. To serve the good of the other art students, Rita introduced her to manga, hoping she'd quit painting and move to Japan, which succeeds. However, this backfires as Mashiro ended up being popular with her manga.
Besides the point, the relationship gets repaired later on. However, even if Rita hated Mashiro for her talent, she still loved her because of her intuitive perspective, and the fact that Shiina regards her as someone special.