Is it permissible for a girl to research and read about sexual culture on permissible websites for the sake of knowledge and learning, even if she is not in need of it or about to get married?

One should not access websites on sexual culture except out of necessity, as doing so involves temptation (fitna) and a waste of time. If these websites contain anything that violates Islamic law, such as nude images or methods that incite lust, then it is absolutely impermissible to access them. Similarly, girls discussing such matters is an entryway for Satan, so one must be cautious and spend time on what is beneficial.