at (one's) elbow
Close by; readily available. Please stay at your mother's elbow, in case she needs your help. I'm not very creative in the kitchen, so I always have a cookbook at my elbow when I prepare a new dish.
at someone's elbow
Immediately beside someone, close by, as in The apprentice was constantly at the master's elbow. Why this idiom focuses on the elbow rather than the arm, shoulder, or some other body part is not known. Moreover, it can mean either that someone is so nearby as to constitute a nuisance or in order to readily provide assistance. Either can be meant in the example above. [Mid-1500s]
at your ˈelbow
very near; within arm’s reach: I always like to have a dictionary at my elbow to check spellings. at (one's) elbow
Close at hand; nearby.