Thanks @nomad-magus for the advice, as far as I am concerned, that is the best advice you can get anywhere.

Your empathy for your sister can land you in the same problem she's currently is.

Instead of empathy, allow your compassion to rule over you, by showing her more love, from there she can learn how to love herself.

All I can see here is that your sister lack the self love, you can't find the love until you learn to self love first, you can't transfer love to others if you lack the love for yourself.

It might not be easily, but you are not helping her with your empathy for her, you can only help her with your compassion for her.