Just let her replace her engine with the one the Steel Watchers use. We are explicitly told it's an improved version of her engine which can survive just fine in Faerun. Then we go to the place where they make Steel Watchers and kill all the Banites and (potentially/probably) liberate the Gondians, who are the ones building the Steel Watchers. It is absolutely deranged to present this as a problem with no win-win solution when you are literally telling players what the solution is and not letting them do it.
