It's a thought, Margaret, but somehow the period of her disappearance coincides with a few years of the <i>strengthening</i> of that folksy trend.
Take this fashion spread from the New York Times of 1951, featuring Tina Leser, Nelly de Grab, Carolyn Schnurer, Rosenfeld and Clifford of del Mar - it's really a massive amplification of things that Ballerino (and, in fact, Leser) started on up to 6 years before:
<img src="http://worldservice.noirboudoir.com/tinaleser/eastmeetswest1.jpg" width=500>
<img src="http://worldservice.noirboudoir.com/tinaleser/eastmeetswest2.jpg" width=500>
A quick glance at Leser's 50s designs shows how much success she continued to have with both authentic and souped up ethnic fabric designs.
I really think it could have more to to with Lizzie's observation, that Ballerino was no longer offering something unique and different - the whole country had copied her, and a handful of better-backed design houses were selling the premium designs, perhaps more successfully.
The atomic/modern design influence coming in didn't necessarily eliminate ethnic or world culture motifs, it just used them in a different way: take this late 50s fabric:
<img src="http://worldservice.noirboudoir.com/orientaliste/persiangardenfull.jpg" width=400 border=2>
Oriental and Mexican motifs did continue at full strength, just everyone else used them too.
I think Ballerino used these features in quite a unique way, but with wider use of them in the 50s, her designs will have got a little swamped.
I'd be really interested to know what she did next. I really wonder if, like Elizabeth Hawes about 15 years earlier, she just upped and transferred her energies elsewhere...
L