It might be best to wait until you are not acutely agitated over your sister's behavior. But not necessarily. I would say you want to be somewhat in control of yourself when you communicate sensitive information. Like the others above, I would cast my vote on the side of letting your daughter in on more of the truth about your family. At age 27, she is well old enough to be allowed to know things that it was appropriate to not share when she was little.

She has a right to work out her own relationship with her aunt. However, what is unbalanced about that is that her aunt has information that she does not. So she is vulnerable to being exploited by her aunt. That's where I think you have a duty to your daughter. At age, 27 your daughter is still naive to much of what one eventually learns in life. I'm not saying: Put an old head on young shoulders. That really can't be done. But there is such a thing as appropriate sharing regarding some of the unpleasant and even shocking truths about life. I believe parents have a role they should play in preparing their adult children for what can come at them in life, especially from older, manipulative, more experienced adults.

I might re-frame your question slightly, and I hope I don't sound presumptuous or condescending. The way you spoke was perfectly natural, but here's my thought: The question is really not so much "Should I tell my daughter about her aunt?" I would frame it as "Should I tell my daughter more about myself, and more about how life operates, and how people operate, and how others may have agendas that she doesn't know about that could imply using her as a pawn in their games?"

You don't want to be interpreted by your daughter as engaging in mean-spirited gossip, just resurrecting past hurts to turn her against someone like her aunt. I very much don't believe that is what you are about. It does sound like your daughter is being "took in" by your sister's slyness. That is partly because she is young and partly because she is not in possession of all the facts, as your sister is. So some calm and careful sharing of some hard to talk about experiences might help her to become a wiser young lady. I would stick to facts and let her draw her own conclusions from them, as she will do anyway. That's why you want to engage her went you are not over-excited.

Don't in anyway press on your daughter to assure you that she understands your pain and/or see's things your way. I would say, "Honey, you will have to make up your own mind about lots of things, but there is a lot you don't know that you are old enough to hear about and, maybe, take into consideration in forming your own judgments."

I've been through the scenario of having a sister who gained control of a parent's finances and the emotional devastation that came in the aftermath of that, where everyone distrusted everyone. It was, and continues to be, a nightmare. And my sister was actually a person with an impeccable history of being the "decent sort." So I hate to think what waits down the road for your family. All I can say is that there is little in life that makes for so much ugliness as conflict over money. Given the past you have already endured, I think it's time to open up some closed closet doors, before there is a flood of new anguish to deal with.