I've taught plenty of intro programming classes. You're likely just a terrible instructor. I've not found a single student that was incapable.
. About a third of the population is simply incapable of abstract reasoning.
Citation needed. What backwater pay-to-publish journal did you find someone that denies that 1/3 of the population fails to reach the the formal operational stage of development?
If you think otherwise, I invite you to come to my house, and I will give you a free dinner while you explain "vectors" to my 15 year old daughter. Good luck with that.
I have a few teaching tricks I've picked-up for that. I have little doubt I could teach your otherwise normal child the basics of vectors in an evening. Well, at least well enough to get her through calc.
Teaching, like programming, is a skill. If you want to better help her, do some reading on formative assessment.