1) Make her motivation to go to Avernus not a sobby "muh engine gonna explode" but "I'm now powerful as hell so I'm gotta rip off the wings of my ex-mistress with my bare hands and eat them with chili"
2) I'm suggesting they rewrite it completely into fun journey of upgrading our fiery friend into avatar of vengeance or\and justice and have her decide what to do with her newfound overtuned powers. Astarion can get his upgrade and so could Karlach. Hell, make it a choice even. Go FULL POWER but become more and more unhinged and demonic so she then decides to go wreck all of Avernus on a quest for vengeance or calm down the engine, maybe even cure it of demonic traces or replace it with weaker non-demonic version or make it HOLY and have her swear an oath to a good deity and become a paladin. Seriously there is so many cool stuff you can think of about what to do with her engine and they chose to drag a pathetic sob story and not even do anything with it.
3) Lock her class to a Fighter (Furious but also Reasonable) and let the player decide her route - upgrade demonic engine to a full power and have her become more unhinged and powerful Barbarian (Vengeance, Avernus ending) or stabilize it, purge it and have her pledge an oath to become a kind and reasonable Paladin (Adventure, Golarion ending)
