I'm going to be bold and say the exact opposite of everyone else: forgiveness is the most important thing you can do. If you don't forgive her, you're the one that will loose out (not on any relationship with her, but the bitterness and resentment that will chip away at your soul). The thing is: you might not be able to forgive her at the moment and that's fine.
Your feelings are important, they are like a compass allowing your gage your reaction to an event. If you are unhappy about something that she did, you need to pinpoint exactly what that is. Once that's done, when you are calm enough to deal with it, I suggest that you meet with her and discuss your feelings and perception of the events. Most of the time things are a big misunderstanding or maybe she acted meanly (or whatever) because she felt threatened, etc. The critical thing is that you can only meet to discuss what has happened once you are calm enough to talk about things in a mature manner: resorting to yelling and arguing is not going to be helpful. You need to be patient and hear her out to. If this is not possible (e.g., she's too immature to discuss things) then I think you have every right to say to her that because she has made you feel this way, you are going to limit the time that you interact which means that you will not be attending any family gatherings where she is present (or whatever you want to do).
Hopefully be discussing it, you'll be able to forgive her at least. It's not about forgive and forget. It's about forgiving because we all screw and moving forwards in a beneficial way. That will hopefully include the forget bit and starting out fresh... but that's not always possible.
And this might take a lot of time to accomplish... forgiveness is hard work, but ultimately it's worth it. I would even go as far to say that forgivenss is necessary, but reconciliation may not be possible.
It might also be helpful to talk to your family members about your feelings and how you felt betrayed and conned into going there when you're not ready to deal with her.
Sorry if this sounds all preachy. In the end it's just my opinion, but this is an issue that is quite close to my heart.
xxx
Will be praying for you! (Unless you write back that you don't want me to!)
