Well welcome to horse ownership, better late than never eh?
OK, same story from me as from most others, this is not the horse for you, and I would strongly advise, how ever much you like her, that you consider selling her and getting something more suitable. I agree with your assessment about her not being bad, just young impatient and headstrong, and to deal with that you have to have a whole lot of experience and different strategies available to you, and because you are a novice, you simply do not have that available to you. It doesn't make you a bad person, it doesn't make her a bad horse, but it does make you a bad match..
It is so easy to reinforce bad behaviour with out even realizing what it was you did. Give you a simple one, I have a new horse, not a beginner horse, she has more spirit than I am used to. I was grooming her in the barn the other day when a door slammed and she spooked, and my very first thought was to pat her and reassure her go to a soothing "there there sweetie, nothing going to hurt you" What I actually did was slap her on the shoulder and tell her to quit. The first response just confirms that it was OK to be a scardy cat, the second says it isn't.
When you are grooming your girl and she looked nasty, put her ears back, did you back off? Did she teach you that this is not comfortable and I can make you quit, or did you carry on, and inspect the area, teaching her that there are no 'out of bounds area'
Your horse sounds smart, and she is probably teaching you all sorts of things about what she wont do..
A total novice needs a forgiving horse, not a smart one, usually an older horse, not a young one, a fully trained horse rather than a baby.
OH, and I don't say any of this lightly as many people here know as an older fairly experienced rider, I bought something way above my competence level, although I could ride I am no trainer, the horse I chose eventually put me in hospital for a month...wrong choices at our age can HURT, a lot.
“Never attribute to malice that which can be attributed to stupidity”