"Almost all" is by no means a stretch....if they didn't straighten it, they covered it. If this weren't the case, why was the Afro such a big deal in the 1960s? Black hair in it's natural UNSTRAIGHTENED state was hardly seen until the 1970s, the proper combs didn't even exist before then that were available to most people. Considering that most people started straightening the hair of children, I say it crossed almost all social and economic strata.
Yes to point #2....and her hair is STRAIGHT, doesn't matter the means. This story is about HOW it's straightened, the means....but it's straight no matter. It conforms to the social norms. She simply used an different means to achieve it. The HOW here is the only unusual thing.
IMHO, this site and others exists because many people of African descent don't know how to care for African textured hair (esp. those US and Europe based) to it's optimum whatever it's state ("relaxed", "hot combed" or "natural")...and the reason for that is people spent 100s of years covering it up and/or disguising it's true texture. In short, we're out of practice and just getting the proper tools.