That social media post apparently mentioned her having a condition called Alopecia, which causes hair loss with some variety in volume.
My guess is that it looked "better" to appear like a Wakandan warrior than trying to hide however many patchy spots she had.
As you said, it's likely that stress exacerbated her hair problem. WebMD exerpt:

Reduce stress. Personal troubles seem to trigger alopecia areata, although this has not been proven scientifically. Telogen effluvium, another form of hair loss, can also be triggered by stress. Learn more about the signs and symptoms of telogen effluvium.