I NEED ADVICE!!!!!! PLEASE, (10 points I'll answer your question)?

[Life]

So, my cousin( and oldest friend) is fighting with me. Let's say her name is Amy, and let's say my other friend is Ella.
Well, it's started after our sophomore year ended, and were now juniors. I asked Amy to come over several times; each time I got told " I'm grounded" or " I'm cruising with my sister". When I went over to Ella's, we would post pictures on facebook(my friend loves taking pictures). Well, not long after Amy found out about it, she would post really childish things. She would post stuff like " I guess I don't have any friends" or (take a picture of her and her little brother) " me and, my new and only friend".
We don't always post pictures, or even get on facebook. But, it never fails every time me, and Ella are together Amy posts something like that.
I feel like Amy see's me as nothing more then a mere third wheel, and that I just keep getting between her and Ella. That and she just wants attention. Then when she puts BFF posts, she includes Candy(who she just met this year), and Ella, but I am always excluded. When me, and Ella confront her about the posts she denies them.
We know there about us , and specifically us alone. Over the summer we went, and saw World War Z( this is after she had posted several things about how we were horrible friends, or that we weren't). Well, Ella posted "Going to see World War Z with the Bestie!!! " to see what Amy would do. Two posts followed.
Then she asked if, we were going to the races the next day we said probably not( she asked Ella actually, and at the time we didn't know if we were). Later on we did, and we saw Amy there. More posts followed. We finally confronted her about it. We were both texting her at the same time. She told Ella that the posts were about us; she was sorry. She told me that they were about other friends. This was within a 5 min range. I've always considered her a friend, but I think I'm nothing to her.

My question is what do I do? Do I just ignore her? Do I just stop altogether talking to them both? Why is she doing this? Is it jealousy? Of who? I hate this, at this rate I would ever better luck never talking again, at least that's how it feels. I feel like I'm just a nuisance.

[FITCH33]

Always follow you're gut feeling and you will allways make the right choice even if it dosent seem to feel good at first but people have the natural instinct to allways do the right thing its just trusting in you're self and it will become apparent after a couple of hard decision that we possess powers that we dont understand but have then its much easier to make snap judgments on the fly