Hermione was shocked when she found out that Narcissa had been unable to decide and then suddenly, with a little bit of input from her, Narcissa finally had!
She tried to tell herself that she likely hadn't had that much influence; perhaps it was more of a case of her input being the straw that broke the camel's back.
"Glad I could help," she said a little bashfully. Unsure what to do next, she stood with her hands folded in front of her.