Omegahugger
Inattentive Idiot
Her reasoning honestly wasn't that bad.
Magic is in many ways a curse that literally twists your soul and just two updates ago we were one poor roll away from literally exploding. Yes, Mathilde was incredibly skilled and loyal to the Van Hals, but Roswita's alternative was a witch hunter who she knew personally and we have no reason to believe he wasn't our equal at the time. Roswita had the choice between an adviser loyal to her specifically and one that was a one bad afternoon away from turning into a hole in reality.
(I would also argue against counting "would've died without our intervention" against her considering what happened to the last Count of Stirland who Mathilde served...)