This could be for a few reasons:
* Time Period and Genre: The Nancy Drew series was written for young readers and aimed for a sense of adventure rather than graphic violence or depictions of physical harm.
* Nancy's Character: Nancy is portrayed as a resourceful and intelligent heroine, so a plot point where she is incapacitated might detract from her character.
While Nancy doesn't get chloroformed, there are instances where she is drugged or unconscious:
* The Secret of the Old Clock (1930): Nancy is drugged with sleeping pills by the villain, but she later escapes and solves the case.
* The Haunted House (1932): Nancy finds herself in a situation where she is nearly overcome by gas, but she manages to escape.
These examples illustrate the dangers Nancy faces, but they also emphasize her resilience and ability to overcome obstacles.
If you're interested in learning more about the Nancy Drew series and the different ways her stories portray danger and adventure, there are many resources available online and in libraries.