Hi rouge, I'm a sober alcoholic, and also have a sister who did enormous damage to her life and family with over drinking. We tried everything, finding her therapy, warning her, making suggestions, nothing worked. Eventually she reduced her intake, but it wasn't anything we did, it was because she met her future husband. Boy were we grateful to him. You didn't cause your sister's drinking, and you can't cure it, and you seem to realise that. But you're correct in thinking it's time to put some boundaries in place.
Set her up with a unique call tone so you don't have to answer at night, or even put your phone on silent. Drunk diallers are a real pain and you have NO obligation to answer. If she's in real trouble she can still call your parents. You can also ask her not to call you when under the influence.
Don't feel you have to keep any secrets for her. Alcoholics love secrecy because it means they don't have to face up to their own behaviour.
You've taken on a lot of responsibility that doesn't belong to you. She's an adult and only she is responsible for her behaviour. Creeping around her, taking her tylenol, keeping her secrets is just enabling her. Step back, make yourself do it, and give her the dignity to find her own recovery.