Sorry, but the story is just some made up stuff. Found the issue the comic was released in on this site, and the Japanese is *completely* different.
This one is good, but the real version is better, imo.
It's basically her being ashamed of her having no hair down there and reading on the net that going without panties stimulates the hair growth. Then the guy tells her that it's the embarrassment that stimulates the growth, and not the act of not wearing panties itself. And her being really gullible believes it, and only finds out way later.