I think it depends on where you live too, skinny (as in thinner than average) being a relative measure.

I live somewhere extremely skinny by global standards and she wouldn't be called skinny, people might say, "yeah I guess she's skinny" if asked, but she wouldn't be seen as "a skinny person" because she wouldn't be far off the average. Same way a 5'8 woman wouldn't be a "tall woman" in the Netherlands.

Yeah I'm around that height and I'd lose my adhd meds if I showed up to a doctor weighing that without a damn good reason

Still seems like a definitional problem, with an imprecise meaning behind the word "skinny."

Even according to BMI, she’s bordering on underweight.

Bordering on, but still on the "normal" side of the chart.

Does "skinny" look to broad population averages, or celebrity averages, or even celebrity averages for that particular age, or some kind of ideal? Is "skinny" a pejorative, negatively loaded term?

I wouldn't call Taylor Swift "skinny" if that's intended to mean thinner than ideal. But she is thinner than the American average. Is the American average considered "fat"? How much of a gap is there between skinny and fat, occupied by people who are neither?

BMI is a terrible metric, and even then her BMI is on the lower end of the normal range.

From the photo she would appear to weight more than 130lbs (for 5 10 height). My one daughter is 130 at 5' 8" and looks much skinnier than TS