The answer to your question would be that the conjunctive adverb that would complete the sentence is the following one: However. Therefore, the sentence would be as follows: Franny wanted to go to Spain; however, she could not afford the exorbitant plane ticket.
"However" is used to introduce a statement that contrasts with or seems to contradict something that has been previously said. In this case, it contradicts with Franny's desire to go to Spain.
"The Yellow Wallpaper" by Charlotte Perkins Gilman. February 25, 2013 By Vocabulary.com (NY) A woman's mind begins to unravel when she is confined to a yellow bedroom after being diagnosed with "a slight hysterical tendency."
