It all happened between 3:05 a.m. and 5:45 a.m.
According to investigators, she set the fires in locations such as a dumpster behind a child care facility, the side of a home, and underneath several other homes.
There were no injuries.
The fires reminded officials of the arson spree in Coatesville, and made the case their top priority.
"When you see seven fires in a little more than two hours in the early morning hours, certainly there's a pattern and certainly we as investigators are concerned about it. That's why there was a full-court press," said Upper Darby Police Superintendent Michael Chitwood.
Authorities have no reason to believe she is connected to the fires in Coatesville.
Police say Gessner was no stranger to firefighters, saying she was often spotted at the scene of other fires in recent days.
"Apparently she sets these fires with a lighter in bush or trash or whatever she coud find," Chitwood said. "When you see, geographically, where these fires are located, they're all located in and around where she lives."
Police say when they caught up with Gessner she was at a Wawa store she was known to hang out, where surveillance tape, they say, captured her singing a strange song.
"She was observed on one of the tapes singing a song, "The fire company will be mad at me, the fire company will be mad at me tonight," Chitwood said.
Gessner has been charged with seven counts of arson, eight counts of recklessly endangering another person, eight counts of risking a catastrophe and related offenses.
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