Susana is an adventurer who abducted Professor Foxe with a sky carriage just before the events of Game 1. It was revealed in Game 4 that she and the rest of her adventuring party were hired to kill him, but instead opted to kidnap him and recruit him for an expedition into the Mournlands.
Susana is the main spellcaster of the group, who used her offensive magic to dish out damage to Monster Squad. Not much is known about her, other than that it is heavily implied that she had relations with Professor Foxe during his kidnapping.
In the Campaign.
Susana made her first appearance in Game 1 when Monster Squad was heading to Morgrave University to meet Professor Foxe. Susana was briefly seen on a rapidly descending sky carriage. Apparently, one of her companions, the half-orc Horty, was an adrenaline junkie who got a thrill out of nearly crashing his vehicle. This sort of behavior endangered lives, prompting Monster Squad to pursue Horty and his allies, including Susana. The chase ended when Susana and co. flew out of sight from Monster Squad.
Susana made her second appearance in Game 4, when Monster Squad raided the abandoned warehouse in an attempt to find Professor Foxe. She primarily attacked Balasar during the fight, though was unable to incapacitate any foes during the encounter. When Betty and Monster Squad talked about a peaceful resolution to the conflict, she was largely silent, only speaking up when she tried to convince Professor Foxe not to leave. She was last seen leaving the warehouse, and she is presumably now on her way to the Mournlands to complete her quest.