Ramkamhaeng or one of the Technics, sure. If you've seen the curricula at those places -- it's like junior high in the non-yellow-shirted world (well, maybe with a bit less independent thinking than junior high). And no one at those schools is from anything other than very humble origins, nor will they break out of that stratum (unless they win the big white lottery).
Must be hiso -- especially if she doesn't just work there, but is employed!
Fucking old farangs is a shit job, and anyone who does it doesn't have many other options in life. Those "educated girls" are pretty much at the bottom of the socioeconomic ladder (where, by the way, most Thai people are, so no shame in that). Same goes for many of those "office girls" you guys are into, but that's a whole nuther story.