Since Cincinnati's move to an executive mayor, the role of vice-mayor has been largely symbolic. When Jim Tarbell was vice-mayor, I seem to recall Mayor Mallory describing him as a cheerleader for the city. David Crowley, while certainly active on Council, seemed to continue the Tarbell tradition of vice-mayor as cheerleader-in-chief.
The appointment of Roxanne Qualls, I suspect, signals a shift in what is expected of the vice-mayor. I can't imagine Qualls signing up for a gig that is merely ceremonial. Instead, it's likely that she has an agreement with Mallory similar to the one Biden had with Obama: that she'll be "in the room" when important decisions are made.
I don't have anything to substantiate my speculation beyond Qualls's history of strong leadership in the city and her penchant for the nuts and bolts of urban policy and planning. If I'm right, though, I think her appointment will be good for both the mayor and the City: her experience and strong voice will be extraordinarily useful to the administration during the difficult months ahead.