How does Aunt Polly's behavior poke fun at some of the medical practices of her time?

Aunt Polly’s remedies are not easy to swallow, as Tom learns the hard way (chapter 12). Tom makes the mistake of mooning around and thinking about the girl he likes, Becky. Aunt Polly notices his unusual behavior and decides he is sick. The crowning blow is a patent medicine called Pain-killer, which tastes so awful that Tom cannot bear to drink it. He feeds it to the cat, whose horrible reaction makes Polly realize that she has been overdoing it and finally desist.
The nineteenth century was the era of “patent medicines,” as people did not yet rely on doctors for everyday minor problems, but many were buying strange concoctions rather than making their own homemade tonics. The manufactured medicines were often largely alcohol but sometimes even contained cocaine or opiates. Aunt Polly had a gullible nature but also was genuinely interested in helping people. Her curiosity and hunger for novelty led her to buying and experimenting with what Twain calls, “all new–fangled methods of producing health or mending it.”
She subscribed to "Health" magazines (which were expensive in those days) and even believed in phrenology, a pseudo-science that diagnosed people by feeling the bumps on their heads. Twain lumps together her “quack periodicals and her quack medicines,” noting they were as likely to kill as to cure.