I can tell you that when I first started working with Lacey, I absolutely hated her, pretty much. She didn't want to be with me and I didn't want to be with her. really the only reason I was working with her was that I didn't want to see a perfectly healthy horse put down because that was her next stop.
I stuck with it thought and now (after three years of tears and trouble), we're basically inseparable.
Looking back I've realized that she wasn't the horse I wanted, she was the horse I needed. She helped me see the areas I needed work in and she helped me round myself out as a person.
Now we really couldn't be more in tune, but back when I got her, I was literally seconds away from giving up on her, multiple times. She wasn't affectionate like I wanted and she didn't seem to need me like I wanted. Now that I am looking back, I can see that she really needed me more than I had any idea and that I just had to learn about interpreting her quiet kind of affection. Through the bond we have, I now have that horse I was looking for and couldn't find, but it did take 3 years.
I don't know, you obviously know her and your relationship better than anyone but I wouldn't really look into selling her before you really examine your relationship. Perhaps you two are too similar (like Lacey and I) and that's what's getting you, or perhaps she has a different "brand" of love than your other horses and you need to readjust to that.
I second what someone said about sending her for more training and then reassessing when she comes home.
And, on the flip side, there's absolutely nothing wrong with finding an animal a new home when it just isn't working out with you. Every animals deserves their "one" and every human deserves their "one" as well and there is no shame in recognizing that you aren't each other's "one".
I wish you luck!
Fabio - 13 year old Arabian/Lipizzan gelding
Rest peacefully, Lacey.