Children of a Lesser God

School superintendent Dr. Curtis Franklin tells teacher James Leeds, referring to janitor Sarah Norman, "She was diagnosed as retarded until she was 7." (0:20)

James tells Sarah, "I don’t know why I became a speech teacher." (0:34)

Sarah and James watch Some Like It Hot in a movie theater. (0:49)

James tells Sarah, "That’s the craziest thing that I ever heard." (0:51)

Student Glen’s father Edward asks Dr. Franklin, referring to Glen, “... change that idiotic haircut?" (0:57)

Poker player: "There goes my mad money." (1:11)

James tells Sarah, referring to a telephone call, "It’s one of the dorm counselors."
”I probably sounded like myself instead of like a dorm counselor sounding like Orin.” (1:14)

James interprets Sarah’s signing: "You feel like an idiot."
”I treat you like an idiot?” (1:26)

Her mother tells Sarah, referring to Sarah’s father, "I hated you for driving him away." (1:37)

James tells Sarah, "It was a shock seeing you in there." (1:50)

A colleague used at least one scene (0:18, 0:23?) from this film to illustrate Avoidant Personality Disorder. And might you consider Schizoid Personality Disorder?

I don't see a Personality Disorder myself. I think Sarah's behavior keeps people at a distance, anger just below the surface, and hurt far below that. She seems to sum it up that way at the end (1:52).