L.W.
Am I reading this right, that she's 33?
She's an adult and old enough to decide what works for her and what doesn't. If it's a problem for her then she alone has the opportunity to change it.
It's hard to see the ones that we love exhibiting behavior that we don't feel is in their best interest. But the truth is that we all have consequences to our actions, and we are the only ones with the power to decide by consequence what we wish to have in our lives and what we don't. We cannot put ourselves in a position of judging someone else's behavior and using our own opinions as our basis for judging.
If this is the biggest problem that your sister has, employ an attitude of gratefulness. We all have our quirks, and she must be a very interesting person if she feels comfortable doing that, and not keeping it a secret from you! lol :)