I thought Ashley gave reasons why Ballade is hard to cast and program generally, but that shouldn't stop the House of Balanchine, particularly since, as abatt notes, the ballet was revived years ago for none other than the company's current Associate Artistic Director. So there are two leading ballerinas around who have danced it, including the one the ballet was made on and as BalanchineFan says, Andersen is still around and about.
Croce wrote a long piece pursuing that theme at the time of the premiere, called, if I remember correctly, "Ashley, Balanchine, and Ballade." From the time frame I'm guessing it would be found in Going to the Dance, don't know if it was included in her final collection. Ashley said in her book that Balanchine read the piece and told her he hadn't been trying to push her in a different direction, but Ashley suspected that he was. I think Croce wrote, "Balanchine is not going to let Merrill Ashley carry on as if she were an uninteresting woman," or words to that effect.