She only falls asleep to her grandmother's songs, and the caregiver doesn't sing

4 month old. My mother sings Rabindrasangeet at every nap and she's out in minutes. On days Dida leaves early, the caregiver tries rocking, walking, patting. Forty minutes of crying. The caregiver is lovely but shy. Says she doesn't know the songs and feels awkward singing. I'm in lab sessions those afternoons. Has anyone moved a sleep cue from one person to another? Would a recording of my mother work, or is it the person, not the song?