Olruggio was hurt/traumatized by fire during his childhood.
- Olruggio encouraged Qifrey to study the magic that scared him the most, and Olruggio himself specializes in fire spells. He also is very concerned about the possibility of contraptions with harmless fire in them possibly fooling people that fire is safe.
Coco's Mother Can't Be Un-Petrified by Licit Magical Means
The spell that turned Coco's Mother to stone originated from a Seal in the spellbook Iguin the Brimhat sold to Coco years before the start of the series. The spell petrified its surroundings indiscriminately, turning both the house and Coco's Mother to stone. Unfortunately, any attempts to reverse the spell that include de-petrifying Coco's Mother could be viewed as a breach of Witch law since all magic performed on the human body is expressly forbidden by the Witches Auditorium (especially healing magic). Qifrey and Coco are already on shaky ground trying to find a copy of the Brimhat spellbook that Coco copied from in order to reverse-engineer the spell, and would likely be punished if anyone on The Council of Magic Security found out about their plan OR the Brimhat's involvement in Coco's Mother's petrification. Qifrey likely knows this and hasn't pointed it out to Coco because his only goal is to trace the spellbook back to the Brimhats. He has no reason to alienate Coco by bringing that fact up, but he also has no reason to help her de-petrify her mother once they've tracked down the spellbook — why leave an obvious trail that points to his involvement when he's worked so hard to conceal his investigation up till now?
Coco will eventually have to choose between upholding the law of Witchkind or freeing her mother by using "illegal" magical means. She'll probably be encouraged to go whole hog on the forbidden magic by the Brimhats, who will offer her the key to freeing her mother when Qifrey and the Auditorium discourage her from doing so.
