Personally I'd keep her on the hook for a) either the transfer fee (the entire fee) or b) finding a new roommate, however long that takes. That seems reasonable if not quite fair from my perspective, as you would unfort. be in charge of the extra bills in scenario (a) but you'd be rid of her much faster.
Having her around sounds like a pain in the ass so personally I'd do with a as long as the bills aren't totally unreasonable without a 3rd person. But it's ultimately your call, and others have made reasonable suggestions as well.
Having her around sounds like a pain in the ass so personally I'd do with a as long as the bills aren't totally unreasonable without a 3rd person. But it's ultimately your call, and others have made reasonable suggestions as well.