Does your sister even recognize openly that there is a drinking problem?
If so, is she old enough to understand that?
You could make a boundary, and tell yourself, "I will send her/give her these things to read..(checklists for al-anon, alcoholic behavior,etc) in order to give her the chance to gain knowledge about what is really happening." Then go HANDS OFF.
That is all you can do. If she chooses to stay in denial, or in an enabling scenario, then she chooses that. and that is out of your control.
If she is a minor, and she is in danger, then you may need to protect her.
Otherwise, if she is an adult, then I would give her the literature/links, then let her figure it out, or ignore it.