OK so update...I took all your advise and put it to test...
She's reared twice since I made this post (worked with her 2 seperate times), and both times I made her back up...FAST as soon as she landed. Not only did she not do it again until the next time I worked with her, but the second one was alot smaller/lower. It's always at the start of whatever I'm doing with her, usually the first time I reach out to clip a lead to her halter. *I bring her into the round pen and turn her loose with the halter on first, then work with her* So she's caught and she knows it, just being silly about me actually "catching" her. I think I'll continue with this method and see how it goes...thank you all for your advise!
I also tried Join-Up with her - went well, her inside ear was glued to me and she was chewing, just didn't get the dropping of her head. But she turned in and took a couple steps towards me, I pat her neck a bit and walked away...she followed
Only for 10-15 minutes since she's only 2, but a start!