Not having read the novel, I can't say for sure, but being familiar
with other works of that era (does anyone else out there read Poe?),
and knowing the conventions of their literary speech, I would say that
St. Clare was playing the piano to the accompaniment of the wind,
sighing in the trees.

Anyone else have other ideas?

Regards,

Bob Loesch
http://www.jps.net/rrloesch