It happened around noontime in the middle of a crowded sidewalk.
Sources say the thieves stole several thousands of dollars in cash as well as jewelry including an expensive diamond brooch.
Authorities say there were as many as ten young men in the group. They reportedly threatened her, but she gave up the valuables and was not hurt.
It is the latest in a series of criminal incidents involving groups of young people on North Michigan Avenue.
In March, police arrested dozens of young men and women who gathered in the area and were allegedly attacking shoppers and police.