A 38-year-old female accountant self-refers after reading about autism in women online. She reports a lifelong history of difficulty understanding social cues, maintaining friendships, and engaging in small talk. She describes having intense, narrow interests — she has spent the past 3 years exclusively reading about Victorian-era postal systems and can recite detailed facts for hours. She reports becoming severely distressed when her daily routines are disrupted, such as when a coworker rearranges shared office supplies. She avoids eye contact because it feels 'physically uncomfortable.' As a child, she was considered 'shy and quirky' but performed well academically. She has developed scripted responses for common social interactions and carefully studies others' facial expressions to determine appropriate reactions. She was previously diagnosed with social anxiety disorder and generalized anxiety disorder. She denies hallucinations, delusions, or mood episodes. Which diagnosis best accounts for her longstanding difficulties?