Why is Miss Stackpole considered an agent in Portrait of a Lady?
Very interesting question. Of course, Henrietta Stackpole is not the only agent, and when you think about it, you can't help but feel pity at Isabel's situation. She is almost "created" into a scientific experiment by her cousin, Ralph Touchett, who engineers his father's will to leave her a massive fortune, so he can see what she does with her life as a result. Then, her two best "friends" in the novel, Madame Merle and Henrietta Stackpole, do not desist in trying to manipulate and influence her to make the choices in life that they would have her make.
Henrietta Stackpole is another character like Caspar Goodwood that represents America's democratic values. She fiercely states that a woman does not need a man to be happy (but then finally marries Mr Bantling, although she clearly has the upper hand in the relationship). She is worried that Isabel will become "corrupted" by her contact with European society and in particular she is worried that she will marry a European and betray her American-ness. She is never subtle in her favouring of Caspar Goodwood as a partner for Isabel Archer (interesting comparison with Madame Merle and Gilbert Osmond) and acts to bring the two together. It is for this, that she can be considered to be an agent in the novel.