She arose at length and opened the door to her sister's importunities. (20)
Big word alert: "importune" means to be overly persistent in asking for something. In that case, all the "importunities" Josephine has been laying upon her sister have been annoying. And so, Mrs. Mallard takes her own sweet time in answering the door.
He stood amazed at Josephine's piercing cry; at Richards' quick motion to screen him from the view of his wife. (21)
Significantly, the reactions and voices that reveal responses to Mr. Mallard's entrance come from everyone except "his wife." Josephine's the one who makes a "piercing cry," not Mrs. Mallard; it's Richards who tries to intercede and stop Mrs. Mallard from seeing him. We don't know how or what Mrs. Mallard would communicate in this moment. It's hidden from us just as Richards tries to hide Mr. Mallard from his wife.