In reading your story one line popped out for me. It was the part about her getting to a place where it's ok to be poly. I read that as ok for her to be poly. In which case, you have an obvious issue.
If I read that right, I'd ask why she needs to be poly? There are many happy mono-poly relationships. The pressure of her adopting your nature may be a major stressor.
If you mean she wants to be ok with you being poly, that's a different issue. Either way, I sense that your patience and her reluctance are producing a lot of stress.
In talking to mono friends, they often have real difficulty understanding that someone can have two or more loves without diminishing them all. Your woman may feel that the OSOs are taking something that is hers. Or she may feel that you are putting more effort into them than her. Or she may be angry at herself because she wants to be supportive, but the adjust is hard, and she thought she was more understanding than that.
On the taking issue, that's a jealousy / possessiveness thing that is covered well in these forums. Look for relevent tags.
The effort issue is easier to deal with. It means that you need to remember that she's an attractive and special girl that needs to be wooed, too. Surprising her with stuff is nice but may seem like you feel guilty. Instead, focus on making sure that you give her as much if not more attention than the OSO. Shave, dress well, and generally primp yourself as though you're going on a date even if you are staying in for the night.
The issue of anger at not adjusting better is much like a self-esteem issue. Be supportive. Comfort her when she struggles. Reassure her when she fears. And most of all celebrate with her when she improves. She may feel you're examining her or judging her for not moving fast enough. Instead, use your observations to find good things. Tell her when you think she's doing well--cheer your partner on.
Your frustration is a you thing. Spilling it on her can be toxic. From some of what you wrote, it sounds like you have a lot of you work to do as well. If I were to hazard a guess, I'd say she's feeling pressure to change, and that pressure is making things worse. The only suggestion I can offer there is that sometimes we have to release the grip and have faith.