As one can imagine, the narrator is sick and tired of being cooped up indoors all day with nothing to do. Above all, she misses human company, the kind of company that Cousin Henry and Julia can provide. One gets the impression that they are stimulating companions, which is just what the narrator desperately needs at this time. Many doctors would agree, but not John. He's convinced that allowing his wife to visit Henry and Julia would be a big mistake:
When I get really well, John says we will ask Cousin Henry and Julia down for a long visit; but he says he would as soon put fireworks in my pillow-case as to let me have those stimulating people about now.
John clearly doesn't want his wife to get over-excited. And he's certain that if Cousin Henry and Julia come over to visit then that's precisely what his wife will become. John's treatment of his wife effectively involves wrapping her up in metaphorical cotton wool so as to avoid anything that might damage her fragile health.
The narrator's not very happy about this, of course, but as always she defers to her husband. Nonetheless, his restrictions make her all the more determined to get well as soon as possible. In that sense, one could say that being deprived of human company has strengthened her character. At the same time, however, the solitude is starting to wreak havoc on her fragile psychological state.
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