My horse back riding lesson horse made riding unbearable....?

And I quit horseback riding awhile back, mostly because of the instructor and frustation at riding that horse .Let me give you some examples and background information. The instructor bought this 20-something year old horse that would not follow any commands, although she had a previous owner. She hardly was even able to when she arrived at the stables. Her first rider was a 9 year old basically training it, which I find astonishing and highly unsafe (the little girl ended up quiting too.) My instructor is a terrific rider and trainer, but refused to take the time to work often with this horse because "she was too uncomfortable, hurt her back, and didn't have the time," as said in the instuctor's own words. The horse was very sway backed to the point of where a trot was spine jolting, and made worse by the horse's nervousness. It was always very irritated, frightened and I had to work hard at CONSTANTLY keeping her head down and relaxed, which she always tried to fling around while foaming at the mouth. I have always kept confidence in myself while riding her, and kept calm which was my instructors main motivation for always putting me on the horse. There was a rainy day when she spooked and tried to run me over. There were countless days where I would have to FIGHT with this horse to pick her hoofs. There was always a thought in my head that at anymore this horse could wipe me off the side of a wall. This is really the only horse she would put me on because I outgrew the rest and I was the only one most experienced to ride her. My question is, am I wrong in thinking that she was trying to kill me? :p but seriously, is this really bad instructing and if I was to continue lessons again, should I not return to her(she's the closest in my area)? Or should i suck it up and see it as riding a difficult horse taught me much more than I would have learned on any other horse?