Math uses symbols heavily as its own jargon, and someone approaching formulae that have unspecified symbols, without knowing this jargon, is typically fruitless.
That said, I agree that math is terribly taught. My mother and my wife both hate math, and talking it out with both of them, I've been able to pinpoint it to a single bad/discouraging (and sometimes straight out mean) math teacher for both of them. Once the teacher is mean or otherwise bad about teaching, they have not only failed as teachers, but have sometimes caused the students to put up mental walls that can be hard to tear down.
I suspect the sister mentioned in the OP may have had such an experience.
I never got math or liked it until I had to do real-world things with it, at which point I dug and managed to teach myself things that I needed. Nearly all my math teachers were horrible. One or two of them seemed almost intentionally obtuse... like they were trying to trick you and taking pleasure in your failure to understand what they were teaching.
That said, I agree that math is terribly taught. My mother and my wife both hate math, and talking it out with both of them, I've been able to pinpoint it to a single bad/discouraging (and sometimes straight out mean) math teacher for both of them. Once the teacher is mean or otherwise bad about teaching, they have not only failed as teachers, but have sometimes caused the students to put up mental walls that can be hard to tear down.
I suspect the sister mentioned in the OP may have had such an experience.