Creation
Mayor Fleming was created by Paul Cornell and was introduced as the Mayor of Metropolis.
Storyarc
After the Dalwythian aliens arrived on Earth, Mayor Fleming chose Jimmy Olsen and Sebastien Mallory to show them the city of Metropolis. Later, Mayor Fleming present the key to the city to Co-Supmerman (aka Jimmy).
Her Fate
It was never revealed what happend to her after the relaunch of 2011. It’s most likely that she was erased because Rob Morrisroe is the new Mayor after the relaunch.