Dealing with Sis

Probably you should see a therapist who can help you learn how to manage this situation properly. Like you said, avoiding her is not an option; and whether or not she knows what she's doing, you can't count on her to make things better.  in most cases like this there are ways you could change your perspective to minimize the amount of grief she causes you - but you'd have to work out with an objective helper based on the specific situations you are facing, your history, your current thinking patterns, your strengths and weakness, etc.  So while I can't give you a simple answer in a forum like this, I am confident that you could learn to manage the situation by seeking further help.