Madame Sofronie is the owner of the hair shop and the author describes her as "large," "white," and "chilly". When she offers to buy Della's hair, she has no concept of how gut wrenching it has been for Della to even consider selling her hair, which is her crowning glory. But she loves Jim so much, she is willing to make this supreme sacrifice. For Madame Sofronie, it is merely a business deal, and she offers Della a only $20 for her beautiful hair.
Sofronie was also the name of a saint in the Romanian Orthodox church, so perhaps when O. Henry says Madame Sofronie "hardly looked the Sofronie" he is really saying that she "hardly looked like a saint." The author may mean it as a contrast - Della and Jim both made hard sacrifices for each other, and saints make sacrifices, but Madame Sofronie is no saint.