In researching my Wicked Joplin book, I turned up no evidence to support this legend. In fact, I can say almost unequivocally that there is no truth to the legend. The main area for prostitution in Joplin from the very early days of the 1870s through the 1910s (shortly before Prohibition put a damper not only on Joplin saloons but also on the town's other vices) was the downtown area, not a street almost one mile west of downtown.
It seems plausible to me to speculate that Maiden Lane probably got its name because during Joplin's early days it was the site of the town's horse racing track in what was then the extreme southwest edge of town. In the world of horse racing, of course, a "maiden" is a horse that has not yet won a race, and there often are races held especially for maidens. The road that we now know as Maiden Lane would have been the "lane" down which the "maidens" would have traveled to reach the race track.
The oval race track to which I referred in the previous paragraph was located at about 17th and Maiden Lane across from the present-day Price Cutter store, and it was built in the late 1870s. However, even in the early 1870s there was a straight one-half mile race track for horses in Joplin that ran on a diagonal from near the entrance of present-day Fairview Cemetery (then called the City Cemetery) to near present-day West Central Elementary School on 7th Street. So, almost from the town's beginning, Maiden Lane was the place for "maiden" race horses.