CarMan,
The things you should consider are :
(1) $$
(2) do you like to have a person stay with you
(3) Do you afraid that only a maid taking care of Elise
(4) Will it be more arguement between you and you sister.
(5) You need to bring Elise to or Your sister pick Elise up.
(6) How come if your sister need to have vacation??