Interested in Language
The context is:
It was not yet midnight, so the outer door to her building hadn't been locked. Inside, it was not much warmer than on the street. She steadied herself and took a moment to catch her breath. She crept up the stairs and gently turned the latch on her family's apartment. Although her right had reached up instinctively to touch the mezuzah on the doorjamb before she slipped inside, she couldn't have said why. She took off her coat, unlaced her boots, and carried them as she tiptoed past the sleeping forms of her mother and father. The apartment was one room, with a dividing curtain the only privacy.
Anyone could help me explain the bold red one? I don't get what the author means, especially "she couldn't have said why". Why she can reach the mezuzah?? pls help.