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.