hi lostfamily-
i'm not sure that YOU need to do anything, other than what you're already doing.
her recovery is her responsibility. let her figure out what to do. she's an adult. she made the choice to drink again. she can figure out what she is going to do.
if it was me, i wouldn't do anything. you are legally separated and you have sole custody of the children. that's really enough for one person to deal with without a fifth child, no?
naive