If it's just because lib dems did badly, that would be rats deserting the ship.
doesnt sound right.
probably something personal.
whatever it is, she ought to consider her position. you guys quite reasonably argue that john should not hold his council seat once he's become an mp. equally, she shouldnt hold it once she no longer represents the party she stood for in getting elected in the first place. she should seek reelection. if she got the seat on her personal merit then she'll win again.