Dear Wish,
It can be done. I had trail ridden for 4 years (once a week, no lessons), then not ridden for nearly a decade, got my first horse–a freshly gelded 5 yr. old Anglo-Arab with three weeks under saddle. I got around 3 months of lessons, then I was on my own. I sporadically got lessons for around 8 years, had to move to a stable where I was the most knowledgable person on riding and training (not that I knew much back then.) My wonderful first horse became super responsive to my aids, and I could still put complete beginners on his back.
The way I did it–I followed Forward Seat, Littauer’s “Common Sense Horsemanship” and other Forward Seat authors.
You ride Western? I greatly recommend “The Schooling of the Horse” by John Richard Young, it is about Western training. This is NOT a book of how to train for modern Western Pleasure show classes, this is a book on how to train a horse that is reliable, calm, responsive, and well prepared to go on to specialized training.
John Richard Young also wrote “Schooling for Young Riders”, another book I highly recommend. It has a very good discussion on how to effectively use a bosal, though most of the riding is hunt seat. It also covers the necessary ground work thoroughly. The author describes, explains, and gives his solutions in detail of how he and his daughter trained a completely bratty spoiled untrained pony stallion (a 2 yr. old not even halter broke to tie). This is the book I would go to when I had an “unsolvable” problem.
Both books are available throught the Amazon web site for less that $10.00 USD each.
Let the wither heal. Be REALLY careful about saddle fit. Not only will you have to worry about saddle fit at first, you are going to have to check the saddle fit and padding at least every six months because, with good riding, her back muscles will grow. Until the wither heals work from the ground, leading, lunging, round pen work, ground driving, you can do LOTS of things with a horse from the ground.
As for riding and training, it can be done, and it will really help if you can draft someone to do cell phone pictures and videos, then you can compare yourself to the pictures in the above books.
Oh, and by the way, I was suffering from my undiagnosed Multiple Sclerosis for my first 22 years of riding seriously when I finally became too disabled to train young horses. It can be done.
Good luck, you have my best wishes.