Term time care is fine as long as you are willing to pay a retainer .. childminder will be well within rights to demand when you don't need her (but probably won't)
Contract is subject to your agreed hours .. I would say most childminders taking a child for 5 hours will charge a whole day if it spreads over lunchtime
no guarantees I don't think .. but if this is her career why don't you talk about it first