The danger in trying to learn roundpenning with a horse with whom you're already having trouble is that you two will get your signals crossed at times. And when that happens with a horse who's not already operating from firm assumption of goodwill and calmness, you are in for Big Trouble.
Either 1) the horse thinks you are retreating from it and becomes more firmly convinced she can/should ignore you, chase you around, and/or come after you.
Or 2) (far more common) you press her too hard and at the wrong moments, and don't back off when you ought, and the horse genuinely thinks you're attacking, and reacts in sincere fear and/or self-preservation. Particularly for horses with feral or semi-feral herd history, you REALLY DO NOT want them reacting to you with fear or self-preservation, no matter how fast you can run and duck, eeep.
Or 3) you alternate too-submissive and too-aggressive/too-unrelenting behavior, and you get all of the above reactions plus the horse becomes more and more convinced that people are unpredictable nutcases to be ignored when possible and defended against with teeth and hooves the rest of the time.
Tact and appropriate body language in the roundpen are not easy to learn from a book or video, you need someone there with you helping you learn, either a very good horseman, or (lacking that) at least a very good experienced charitable fully-comprehending horse.
This situation has neither.
Look, the mark of a good horseman is to know what you can safely and sensibly do yourself, and what you (as yet) cannot. Really truly. It is time to get help, and the longer you delay the harder it's going to be to find anyone good enough TO help you. When you can't find anyone good enough to help you, that's when the horse becomes whatever today's alternative to dogfood is (there are many other sorts of sad ends for messed-up horses).
Pat, who has seen a number of horses meet that sort of sad ends, labelled as 'outlaws' or 'nutcases', by means of stories that begin like this one, despite all the owner's best intentions.