The average height of a 12 year old child..boy or girl…is 54 to 64” (137 to 162cm) with girls being a little bit taller at that age. As shown above, most adult females don’t get much taller than a child of 12 years old.
Your child is that high? Unless you child is a teen who has already done their puberty growth, you might want to get them checked by your doctor for gigantism or other similar hormonal disease.
You seem to be missing the point that most women in the US have an average height of a 12 year old child.
You don't seem to understand that:
You can't size a sloped top tube frame by looking at the "seat tube length". You can see in the above diagram, there are five frames which are exactly the same effective size, but depending on the slope of the top tube on that particular random frame, the seat tube can be five different "lengths".
You are completely missing the point. “Frame size” harkens back to the days when the seat tube length was actually, say, 15” (43cm) long. Yes, the actual “seat tube length” varies today but a frame that is marked as a “43cm” is going to have similar proportions…including reach…of that old 15” frame.
And note, that in your diagram, the reach doesn’t change just because the seat tube length does.
“I’ll take ‘things that people don’t say anymore’ for $500.” No one really said that back when frames used horizontal top tubes. They asked for a certain frame size. Salespersons would..and still do…ask for the person’s height and perhaps inseam as a starting point for fitting a bike. They most certainly don’t ask for the person’s “reach” because even experienced cyclists probably don’t know what their reach is.
As someone who regularly sells bikes to people, I start with height and inseam. I have them stand over the bike and see how much room they have to avoid smashing and delicate bits on the bike. I then have then sit on the bike and see how “stretched out” they are (in other words, the “reach”). I then have them ride the bike while I watch them. I might suggest a different bike if they say they feel too stretched out or if I see that they look too stretched out.
That picture is what far too many adult women have had to deal with in the past. Things are better today but only slightly since bike manufacturers still cater to adult males for the most part.