I was dependent on alcohol in the past (wine and/or vodka).
Here are some things my boyfriend (now husband) said that was helpful in changing my habits
1, "honey, I know you enjoy it but after a while all it will do is make you feel.sick"
2, "How about just giving your self a night off the booze, have some wine tomorrow night" - (the next night encourage me not to drink.)
3, "do you want to talk instead of drink? We can only talk if you have a diet coke instead"
In terms of practical thing your sister can do is -
Go to bed early too avoid over drinking.
Make a "to do list" for stuff she needs or wants to do even watching a movie. It's amazing how much time you waste while drinking.
I hope some of what I have suggested is helpful.
Try not to worry too much I reckon this is a temporary problem and she (unlike me) acknowledged that she has a problem and that's half the battle.