If anything, the character's instransigence is an opportunity for Sorshen to do the thing which the passage of time has largely rendered impossible (and in my eyes renders her all but irredeemable): make amends and restitution to one of her victims.
That could be interesting, but probably not something demanded by her Oath or her devotion to Lissala. Another issue is she is a fanatical servant of First King Xin - she is currently very sad about having to oppose Xin's mad ghost in the finale of Shattered Star - and Xin has reason to hate Sorshen as one of the leading Runelords who assassinated him. That apart from the PC's resentment at being used as a battery for 11,000 years.
I could imagine the PC ending up working with Sorshen against even worse Runelords like Zutha, who IMC is free at full power and ruling Belkzen, about to conquer Lastwall with his orc and undead legions. I think that could be cool, but certainly not something I would force on the PC. The PCs already rejected overtures from Runelord Krune, who is likewise free and ruling Kaer Maga as his new capital.