Yes, she is. She's my baby cousin but always has been really mature for her age and very independent and confident in her own style/opinions. She's like my sister, because we grew up together.
HOWEVER, she's pissed at me right now and hasn't really spoken much to me in a year (I moved away to live with my new boyfriend last year, right in the middle of a quilting project we'd been doing together, etc.).

I've apologized, but she got mad at me for being so impetuous and moving in with my boyfriend SO fast that I think that made her more mad than losing my companionship.
Any ideas?
You may be now seen as unpredictable to her, in which unpredictability = unaccountability. And, for her, it might be hard to wrap up trust in unpredictability, by the very nature of what it is. So, she's letting her emotions fuel her stubborn righteousness, holding on to the hurt allows her to manifest it in ways that could then hurt you....so you may understand the hurt you've caused her. (all this, not as conclusive, but, how she may view things). My best friend, ESFJ, can be very fickle, but, only because she doesn't like letting others down, so she over-commits, and then has to back out. However, she abhors fickleness in intimate relationships, she wants to be very clear on where she stands, in terms of another's feelings for her. And, when a person crosses that line, in her mind, her hurt is very deep and often times, rather than deal with the situation...she rather not deal with the person. Her emotions overwhelm her sometimes, so she retreats. And, finally, changes, life changes, changes in people close to her (which affects, in indirect ways, her own life), are hard to handle for my friend, esp. when she only gets to be 'privy' of the changes at the end. Like she was left out because the other doesn't care to include her. I'd say you try to reach out to her, consistently, not allow her to push you guys away, and every time you reach, add in what makes you twos relationship 'special' to you...give her grounding of the old/the familiar. And, if you can think up of a way, try to make up for the quilting project. Maybe each month mailing the quilt back and forth until finished? To show her your new life (and love) are not replacing the old?
Btw, the dish turned out pretty good, and since the mom was there, we added chicken. AND, the whole family was able to ingest it without making funny faces. I'd say that's success.
