Flaring was a character that was introduced in Mortal Coil. She was a senior member of the Irish Sanctuary before its destruction, but wasn't there that day and went on to attend the Council Elections.
Flaring was present at the election of the new Grand Mage. She mentioned that both Charivari and Keratin, two dark sorcerers, hated Ireland and were plotting against it at every moment. She was later possessed by a Remnant in China's Library.
Flaring is based on a fanfiction writer under the pen name "Flaring Rhythm", who was added (along with her close friend Shakra) after having a debate with Derek Landy over Twitter about the pairing she was obsessed with - Valduggery - to see if it would be featured in the books.