Unlike document-level AI-generated text (AIGT) detection, sentence-level AIGT detection remains underexplored, despite its importance for addressing collaborative writing scenarios where humans modify AIGT suggestions on a sentence-by-sentence basis. Prior sentence-level detectors often neglect the valuable context surrounding the target sentence, which may contain crucial linguistic artifacts that indicate a potential change in authorship. We propose **GL-CLiC**, a novel technique that leverages both **G**lobal and **L**ocal signals of **C**oherence and **L**ex**i**cal **C**omplexity, which we operationalize through discourse analysis and CEFR-based vocabulary sophistication. **GL-CLiC** models local coherence and lexical complexity by examining a sentence’s relationship with its neighbors or peers, complemented with its document-wide analysis. Our experimental results show that **GL-CLiC** achieves superior performance and better generalization across domains compared to existing methods.