Other way around, she was his mentor as a summer associate
"Robinson met Barack Obama when they were among the few African Americans at their law firm, Sidley Austin LLP (she has sometimes said only two, although others have noted ut there were others in different departments).[55] She was assigned to mentor him while he was a summer associate.[56] Their relationship started with a business lunch and then a community organization meeting where he first impressed her.[57]"
"Robinson met Barack Obama when they were among the few African Americans at their law firm, Sidley Austin LLP (she has sometimes said only two, although others have noted ut there were others in different departments).[55] She was assigned to mentor him while he was a summer associate.[56] Their relationship started with a business lunch and then a community organization meeting where he first impressed her.[57]"
https://en.m.wikipedia.org/wiki/Michelle_Obama