I think assist feedings need to be reserved for when it will not eat at all. If it will eat Live, then feed it live. I understand personal preferences and not wanting to feed off a live animal, but which one is more important to you? Your snake or the feeder mouse (that'll end up fed off to someone else's snake anyways).

I would feed it live a few times, to get her eating and back up to size then you can give F/T another shot.