I think some whiny people are that way all their lives, it's part of their character. Sorry your sister is that way. My husband's first wife is that way. Everyone had a joke, don't ask her "how are you?" or she'd tell you in infinite detail. It's impossible to get her off the phone or get a word in edgewise, etc. Some people don't "do" enough in their own lives so don't have much to talk about except complaints and other people's doings, etc. But it's hard to get someone else to pay attention to our "don't do that," people have to make their own mistakes (but then it's hard to have them complaining on and on after you told them and knew it would be a mistake :-)

I would just practice not getting "sucked in" by your sister anymore and her dramatics; I'm glad you have your husband and others helping you. It is sad you've listened to and helped her in the past and now she can't understand she's not there for you.